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Background: Neratinib (N) is a potent irreversible inhibitor of HER1, HER2, and HER4 and has been shown to have antitumor activity in patients (pts) with human epidermal growth factor receptor 2 (HER2) - positive breast cancer. A previous study of combination of neratinib with capecitabine (X) was associated with > G 3 diarrhea in > 20% of patients. Currently, the NALA study is evaluating this combination of N with X at standard schedule against control. X at 7 day on and 7 day off schedule (7/7) has been shown to be well-tolerated with less ≥G3 toxicities. We are conducting a phase Ib/II study of N with X (7/7) in pts with pretreated HER2+ MBC (NCT03377387). Methods: Eligible pts had HER2+ MBC, normal left ventricular ejection fraction (LVEF ≥ 50%); pts can have any and up to 4 prior chemotherapy-based treatments in phase Ib and II portions, respectively. Primary endpoints are to define maximum tolerated dose and efficacy in phase I and phase II portions, respectively. Secondary endpoints include safety and tolerability; exploratory endpoint is to quantify cell-free DNA to correlate with response for phase II portion. There were 4 cohorts for phase Ib with dose level 1 with starting dose of X at 1500 mg BID at 7/7 schedule with N at 240 mg daily. Results: As of July 1, 2018 8 pts have been enrolled in 2 cohorts. The median age is 63y (range: 57-79), and median ECOG is 0 (range: 0-1). 4 patients were treated at dose level 1 and 2 of 4 patients experienced dose-limiting toxicity with G3 diarrhea during cycle 1. Other significant toxicities included G3 hand foot syndrome (n=1), G3 fatigue (n=1) and G3 nausea (n=1). Three pts have now been treated at dose level -1 (X at 1000 mg twice daily 7/7 and N at 240 mg daily) and no ≥ G3 toxicities has been noted. Once MTD is reached, the phase II portion will occur to assess the efficacy and to further establish the safety and tolerability of capecitabine and neratinib at the MTD. Conclusions: The phase Ib/II study combining neratinib and capecitabine 7/7 is ongoing and updated result will be presented. Citation Format: Wang R, Singh J, Sterlin V, Goldstein M, Lake D, Wong S, Baselga J, Norton L, Dang C. Phase Ib/II study of capecitabine 7/7 schedule with neratinib in patients with HER2-positive metastatic breast cancer (MBC) [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P6-18-30.

Background DS-8201a is a HER2-targeting antibody-drug conjugate with a high drug-to-antibody ratio of 7 to 8. A novel cleavable peptide-based linker joins the humanized HER2 antibody to a topoisomerase I inhibitor payload. In an ongoing phase 1 study (J101), DS-8201a was tested at doses of 0.8 to 8.0 mg/kg and tolerated with no predefined dose-limiting toxicities; 5.4 and 6.4 mg/kg doses were recommended for expansion. Subjects with HER2-positive breast cancer (BC) treated at these 2 doses had an overall response rate (ORR) of 54.5% (54/99). The phase 2 DESTINY-BREAST01 trial began enrollment in August 2017 with a dose-finding stage, including 5.4, 6.4, and 7.4 mg/kg. To determine the recommended dose for continued development in HER2-positive BC, a comprehensive analysis of observed data and exposure-response (ER) from both trials was performed. Methods A population-PK (PPK) model was developed using data from all subjects with available concentration data. Individual exposure parameters (Cmin, Cmax, AUC) were estimated from the PPK model and used in the ER analyses. ER analyses were conducted using logistic regression or Cox proportional hazard modeling for efficacy (ORR, duration of response, and PFS) and safety (nausea, diarrhea, left ventricular ejection fraction, neutropenia, anemia, thrombocytopenia, dose reductions due to TEAE, discontinuations due to TEAE, and interstitial lung disease [ILD]). Results As of 18 Apr 2018, in J101, there are 111 HER2-positive BC subjects treated at 5.4- or 6.4-mg/kg doses. As of 25 Apr 2018, DESTINY-BREAST01 enrolled 65 HER2-positive BC subjects across 3 doses (5.4, 6.4, and 7.4 mg/kg). Confirmed ORRs in J101 for HER2-positive BC subjects at 5.4 and 6.4 mg/kg were 52.6% (20/38) and 55.7% (34/61), respectively. In J101, AEs Grade ≥3 were reported in 35.6% (16/45) at 5.4 mg/kg and 50% (33/66) at 6.4 mg/kg. The relationship between DS-8201a intact Cmin and ORR was statistically significant (P=0.035). There was a trend of improved PFS with higher intact exposures (P=0.238). Statistically significant relationships were observed between exposures and the following safety endpoints based on logistic regression: neutropenia (any grade, P=0.003; Grade ≥3, P=0.037), anemia (any grade, P=0.002; Grade ≥3, P Conclusions In J101, DS-8201a demonstrated an acceptable safety profile and high response rates in HER2-positive BC at both doses. The ER analyses showed a statistically significant relationship between exposures and ORR (with a trend for higher PFS at higher doses), as well as exposures and risk of key adverse events. Considering the predicted benefit/risk profile, 5.4 mg/kg is the recommended dose for continued development of DS-8201a in the DESTINY-BREAST01 trial and in phase 3 clinical trials in HER2-positive BC. Citation Format: Tamura K, Modi S, Tsurutani J, Takahashi S, Krop IE, Iwata H, Wada R, Yin O, Garimella T, Sugihara M, Zhang L, Lee C, Yver A, Baselga J. Dose justification for DS-8201a, a HER2-targeted antibody-drug conjugate, for HER2-positive breast cancer: Observed clinical data and exposure-response analyses [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P6-17-10.

Background: The oral AKT inhibitor IPAT is being evaluated in cancers with a high prevalence of PI3K/AKT pathway activation. In the PBO-controlled randomized phase II FAIRLANE trial (NCT02301988), adding IPAT to PAC as neoadjuvant therapy for TNBC led to a numerical increase in pathologic complete response (pCR) in unselected patients (17.1% vs 13.3%), with a greater treatment effect in patients with PIK3CA/AKT1/PTEN-altered tumors (17.9% vs 11.8%). The addition of IPAT also led to an increase in complete response (CR) by MRI (27.6% vs 13.3%) that was enhanced in patients with PIK3CA/AKT1/PTEN-altered tumors (39.3% vs 8.8%) [Oliveira, AACR 2018]. We report an exploratory analysis performed to provide better understanding of potential biomarkers for response. Methods: Pretreatment tumor samples were evaluated for genomic alterations using the FoundationOne® (Foundation Medicine) assay (n=144) and gene expression by RNA-Seq (n=92). Samples were classified into TNBC subtypes based on the method developed by Lehmann and Pietenpol [Lehmann, J Clin Invest 2011]. Tumor-infiltrating lymphocytes (TILs) were quantified using the Salgado method [Salgado, Ann Oncol 2015] (n=135). Results: Of 62 patients (43%) with PIK3CA/AKT1/PTEN-altered tumors, 21 had an activating mutation in PIK3CA or AKT1 and 47 had an alteration in PTEN (6 [3 in each arm] had both PIK3CA mutation and PTEN alteration). Although only 3 patients with PIK3CA/AKT1-mutant tumors achieved a pCR, there was an increased rate of MRI CR with the addition of IPAT to PAC [Table]. In patients with PTEN alterations, both pCR rate and MRI CR rate were increased with IPAT. In patients treated with PBO + PAC, all 4 pCR patients evaluable by RNA-Seq were of the immunomodulatory (IM) subtype. However, in the IPAT + PAC arm, pCRs were also seen in patients with basal-like 1 (BL-1), mesenchymal (M), and mesenchymal stem-like (MSL) subtypes. Consistent with this observation, in the PBO + PAC arm, samples from patients achieving a pCR had significantly higher levels of stromal TILs than those from patients who did not have a pCR, while no difference was observed in the IPAT + PAC arm. Response, n (%)PIK3CA/AKT mutation (n=21)PTEN alteration (n=47) IPAT + PAC (n=11)PBO + PAC (n=10)IPAT + PAC (n=21)PBO + PAC (n=26)pCR1 (9%)2 (20%)4 (19%)3 (12%)CR by MRI5 (45%)1 (10%)8 (38%)2 (8%) Conclusions: This retrospective exploratory biomarker analysis of the phase II FAIRLANE trial of neoadjuvant IPAT for TNBC provides insight into the potential heterogeneity of response and resistance to taxane therapy. The results also hint that response to PAC alone is dependent on baseline immune infiltration and that this dependency might be relieved with the addition of AKT inhibition. Citation Format: Wongchenko MJ, Oliveira M, Saura C, Nuciforo P, Calvo I, Andersen J, Passos Coelho JI, Gil Gil M, Bermejo B, Patt DA, Ciruelos E, Singel SM, Maslyar DJ, Xu N, de la Peña L, Baselga J, Gendreau S, Isakoff SJ. Exploratory biomarker analyses of FAIRLANE, a double-blind placebo (PBO)-controlled randomized phase II trial of neoadjuvant ipatasertib (IPAT) + paclitaxel (PAC) for early triple-negative breast cancer (TNBC) [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P2-08-19.

Altres ajuts: European Research Area-NET, Transcan-2 (AC15/00063), Asociación Española Contra el Cáncer (LABAE16020PORTT) i AIOC15152806CRUZ, Generalitat de Catalunya(PERIS, SLT002/16/00477 En el cas dels drets, per a usos comercials contactar amb: journals.permissions@oup.com BRCA1 and BRCA2 (BRCA1/2) -deficient tumors display impaired homologous recombination repair (HRR) and enhanced sensitivity to DNA damaging agents or to poly(ADP-ribose) polymerase (PARP) inhibitors (PARPi). Their efficacy in germline BRCA1/2 (gBRCA1/2)-mutated metastatic breast cancers has been recently confirmed in clinical trials. Numerous mechanisms of PARPi resistance have been described, whose clinical relevance in gBRCA-mutated breast cancer is unknown. This highlights the need to identify functional biomarkers to better predict PARPi sensitivity. We investigated the in vivo mechanisms of PARPi resistance in gBRCA1 patient-derived tumor xenografts (PDXs) exhibiting differential response to PARPi. Analysis included exome sequencing and immunostaining of DNA damage response proteins to functionally evaluate HRR. Findings were validated in a retrospective sample set from gBRCA1/2-cancer patients treated with PARPi. RAD51 nuclear foci, a surrogate marker of HRR functionality, were the only common feature in PDX and patient samples with primary or acquired PARPi resistance. Consistently, low RAD51 was associated with objective response to PARPi. Evaluation of the RAD51 biomarker in untreated tumors was feasible due to endogenous DNA damage. In PARPi-resistant gBRCA1 PDXs, genetic analysis found no in-frame secondary mutations, but BRCA1 hypomorphic proteins in 60% of the models, TP53BP1 -loss in 20% and RAD51 -amplification in one sample, none mutually exclusive. Conversely, one of three PARPi-resistant gBRCA2 tumors displayed BRCA2 restoration by exome sequencing. In PDXs, PARPi resistance could be reverted upon combination of a PARPi with an ataxia-telangiectasia mutated (ATM) inhibitor. Detection of RAD51 foci in gBRCA tumors correlates with PARPi resistance regardless of the underlying mechanism restoring HRR function. This is a promising biomarker to be used in the clinic to better select patients for PARPi therapy. Our study also supports the clinical development of PARPi combinations such as those with ATM inhibitors.

Background Diarrhea is the most commonly reported adverse event (AE) on pertuzumab (Ptz) in both early and metastatic breast cancer (BC) settings. We report safety analyses of diarrhea from the large adjuvant APHINTY study in HER2 positive early breast cancer (EBC). Patients and methods In this exploratory analysis, the safety population included 2364 patients in the Ptz arm and 2405 in the placebo (Pla) arm. No specific prophylaxis was mandated by the protocol, however early intervention with loperamide as well as fluid and electrolyte replacement was recommended. Diarrhea incidence, severity (NCI-CTCAE v4.0), onset and management were analyzed. Results Diarrhea was the most common AE in the Ptz arm (71.3% vs. 45.2% in the Pla arm) and the events were mostly G1. Diarrhea ≥G3 was observed in 9.8% and 3.7% in Ptz and Pla arms, respectively. The highest incidence was reported during administration of HER2 targeted therapy and taxane (61.4% vs. 33.8% with Ptz and Pla, respectively) with a marked decrease observed upon chemotherapy cessation (18.1% vs. 9.2% with Ptz and Pla, respectively). The median time from first targeted treatment to onset of diarrhea during the chemotherapy phase was 7 and 10 days (Ptz/Pla). On average, diarrhea events lasted longer in the Ptz than in the Pla arm (median 8 vs. 6 days). Diarrhea events were more frequent with the administration of docetaxel + carboplatin and targeted agents, irrespective of the severity. Detailed results are reported in Table 1. Conclusions In the curative setting, diarrhea due to Ptz was mild, generally manageable with common antidiarrheals and did not affect patients' ability to receive treatment. The APHINITY findings are consistent with the well-characterized pattern of pertuzumab-related diarrhea across the HER2 BC spectrum. Diarrhea incidence, severity (NCI-CTCAE v4.0), onset and management Ptz, n=2364Pla, n=2405Incidence and severityTotal number of patients with at least one adverse event$1685 (71.3%)1086 (45.2%)Total number of events$34151792NCI CTC AE Grade (highest grade per patient)!n1683 (71.2%)1085 (45.1%)Grade 1829 (35.1%)690 (28.7%)Grade 2622 (26.3%)305 (12.7%)Grade 3229 (9.7%)90 (3.7%)Grade 43 (0.1%)0Onset and duration$Median time (days) from 1st HER2 targeted treatment to onset (min-max)7 (1 – 358)10 (1 - 384)Median Duration (days) of each event (min-max)8 (1 - 811)6 (1 - 1022)ManagementAntidiarrheals$898 (38.0%)386 (16.0%)Dose modification* of any study drug!210 (8.9%)74 (3.1%)Dose modification* of HER2 targeted treatment!69 (2.9%)18 (0.7%)Discontinuation of any study drug!38 (1.6%)7 (0.3%)Discontinuation of HER2 Targeted treatment!20 (0.8%)2 ( Citation Format: Bines J, de Azambuja E, Zardavas D, Procter M, Restuccia E, Viale G, Suter T, Arahmani A, van Dooren V, Clark E, Eng-Wong J, Gelber R, Piccart M, von Minckwitz G, Baselga J. Incidence and management of diarrhea with adjuvant pertuzumab and trastuzumab in HER2-Positive breast cancer [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P1-13-07.

Background: The oral Akt inhibitor IPAT is being evaluated in cancers with a high prevalence of PI3K/Akt pathway activation. In the placebo-controlled randomized phase II LOTUS trial (NCT02162719), adding IPAT to PAC as first-line therapy for metastatic TNBC improved progression-free survival (PFS) in unselected patients (hazard ratio [HR]: 0.60 [95% CI: 0.37–0.98]), with a more pronounced effect in patients with PIK3CA/AKT1/PTEN-altered tumors (HR: 0.44 [95% CI: 0.20–0.99]) [Kim, Lancet Oncol in press]. An exploratory analysis was performed to understand better the potential associations between PIK3CA/AKT1/PTEN alterations and other biomarkers relevant to TNBC, as well as IPAT efficacy. Methods: Pretreatment tumor samples (76 primary, 27 metastatic) were evaluated for genetic alterations using the FoundationOne® (Foundation Medicine) assay (n=103) and gene expression by RNA sequencing (n=73). Tumor-infiltrating lymphocytes (TILs) were quantified using the Salgado method [Salgado, Ann Oncol 2015] (n=118). Samples were classified into subtypes by gene expression based on the method developed by Lehmann and Pietenpol [Lehmann, J Clin Invest 2011]. Results: Of 42 patients (41%) with PIK3CA/AKT1/PTEN-altered tumors, 26 had an activating mutation in PIK3CA or AKT1 and 16 had an alteration in PTEN. Patients with PIK3CA- and AKT1-mutant tumors were enriched in the BL2 and LAR TNBC subtypes, whereas those with PTEN-altered tumors were enriched in the BL1 subtype. An internal analysis of the publicly available METABRIC dataset yielded similar results. PTEN alterations were also associated with reduced levels of stromal TILs compared with PIK3CA/AKT1-mutant and PIK3CA/AKT1/PTEN non-altered tumors. In an exploratory analysis of the 26 patients with PIK3CA/AKT1-mutant tumors, the effect of adding IPAT was particularly pronounced (PFS HR: 0.24 [95% CI: 0.06–0.83]; median PFS 12.9 months in the IPAT + PAC arm vs 5.0 months for placebo + PAC); interpretation of efficacy in patients with PTEN-altered tumors was limited by the size of the subgroup. There was no enrichment of PIK3CA/AKT1/PTEN alterations in metastatic vs primary samples, nor in samples collected after (neo)adjuvant chemotherapy vs from chemotherapy-naïve patients. Additionally, there was no association between PIK3CA/AKT1/PTEN alterations and BRCA1/2 alterations. BRCA1/2 alterations were not associated with any differences in IPAT efficacy outcomes (PFS, objective response rate). No association was observed between PIK3CA/AKT1/PTEN-altered status and gene signatures of immune cell infiltration/activation or tumor mutational burden. High (≥10%) vs low levels of stromal TILs showed a trend toward longer PFS in patients treated with placebo + PAC (HR: 0.74 [95% CI: 0.39–1.48]), but no difference was apparent in those treated with IPAT + PAC (HR: 1.14 [95% CI: 0.57–2.40]). Conclusions: This retrospective exploratory biomarker analysis of the phase II LOTUS trial of IPAT in TNBC provides insight into the potential heterogeneity of disease biologies underlying PI3K/Akt pathway activation. Citation Format: Wongchenko MJ, Dent R, Kim S-B, Saura C, Oliveira M, Baselga J, Kapp AV, Chan WY, Singel SM, Maslyar DJ, Gendreau S. Biomarker analysis of the LOTUS trial of first-line ipatasertib (IPAT) + paclitaxel (PAC) in metastatic triple-negative breast cancer (TNBC) [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P2-09-20.

Background A-to-I RNA editing, a post-transcriptional modification of the RNA catalyzed by the ADAR family of enzymes, is emerging as a widespread phenomenon in breast cancer (BC). A-to-I RNA editing is more frequent in the highly repetitive Alu regions but can affect both coding and non-coding regions. It has been shown to greatly impact cell functionality. In a recent report, we have shown that A-to-I RNA editing is regulated both by ADAR copy number and type I interferon response (Fumagalli et al. Cell Rep 2015). The main aim of the current study was to investigate the extent and profile of A-to-I RNA editing in HER2+ BC patients (pts) treated in the NeoALTTO trial, and to explore its impact on pathologic complete response (pCR) and survival. Methods Aligned RNAseq reads of sufficient quality and quantity were obtained for 252 of the 455 pts enrolled in the study, as described previously (Fumagalli et al. JAMA Oncol 2016). Editing sites from the rediPortal database were assessed. The editing level at a given site was computed by counting the number of Gs and As. Sites with coverage more than 10 were considered for further analyses. Editing in normal tissues was obtained from the GTEx project of the rediPortal database. Tumor infiltrating lymphocytes (TILs) and copy number aberrations were previously reported. Correlations between different parameters were assessed using Spearman correlations (ρ). The Mann-Whitney test was used to relate binary and numerical features. Event-free survival (EFS) analysis was performed using the Cox proportional hazard model. Results There was a median of 71470 edited sites per sample. As expected, mean editing per sample correlated with ADAR expression (ρ=59%, p Conclusions Our study shows for the first time that deregulated RNA editing, as compared to editing in normal tissues, is a widespread phenomenon in HER2+ BC patients treated in the NeoALTTO trial and is associated with poor outcome. These results may provide new perspectives for the treatment of HER2+ disease by developing therapies targeting RNA editing. Citation Format: Venet D, Rothé F, Dupont F, Maetens M, Fumagalli D, Salgado R, Bradbury I, Pusztai L, Harbeck N, Izquierdo M, de la Pena L, Ignatiadis M, de Azambuja E, Huober J, Nuciforo P, Baselga J, Piccart M, Loi S, Sotiriou C. Deregulation of A-to-I RNA editing is associated with poor prognosis in HER2+ breast cancers in the neoALTTO trial [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P2-05-04.

Background: BELLE-2 (NCT01610284) met its primary endpoint of a statistically significant improvement in progression-free survival (PFS) with the pan-phosphoinositide 3-kinase (PI3K) inhibitor BUP+FUL compared with PBO+FUL in postmenopausal pts with HR+, HER2– ABC (Baselga et al. Lancet Oncol 2017). Here, we report the final results for OS. Methods: Postmenopausal women with HR+, HER2– ABC refractory to aromatase inhibitors were enrolled in this randomized, double-blind, placebo-controlled, Phase III study. Pts were randomized (1:1) to receive either oral BUP (100 mg/day) or PBO plus intramuscular FUL (500 mg per standard of care). Randomization was stratified by PI3K pathway status in archival tumor tissue (activated [PIK3CA mutation or loss of phosphatase and tensin homolog expression], non-activated or unknown) and visceral disease status (present or absent). Baseline PIK3CA mutation status in circulating tumor (ct) DNA was assessed in a subset of pts. The key secondary endpoint was OS, defined as time from randomization to date of death due to any cause, in the full population (PI3K pathway activated, non-activated and unknown), main study cohort (PI3K pathway activated and non-activated) and PI3K pathway-activated subpopulation. Other secondary endpoints included safety. OS by PIK3CA status in ctDNA was also investigated. Results: 1147 pts received BUP+FUL or PBO+FUL. In the full population and main cohort, OS results trended in favor of BUP+FUL vs PBO+FUL, but were not statistically significant (Table). Post-treatment use of antineoplastic medications was balanced between both arms. In pts with PI3K pathway-activated status, OS improved by approximately 6 months (Table). In pts with mutant PIK3CA ctDNA status, there was a slight trend in favor of BUP+FUL vs PBO+FUL (Table). Median OS, monthsHR (95% CI)P valueFull population N=1147BUP+FUL n=57633.20.87 (0.74–1.02)0.045* PBO+FUL n=57130.4 Main cohort n=851BUP+FUL n=42730.90.91 (0.75–1.09)0.144* PBO+FUL n=42428.9 PI3K pathway activated n=372BUP+FUL n=18833.60.81 (0.61–1.08)0.075** PBO+FUL n=18427.5 ctDNA PIK3CA mutant n=200BUP+FUL n=8726.00.81 (0.56–1.17)0.127** PBO+FUL n=11324.8 ctDNA PIK3CA non-mutant n=387BUP+FUL n=19931.41.12 (0.83–1.50)0.774** PBO+FUL n=18836.8 *One-sided P value. **Nominal P value. The safety profile of BUP+FUL was consistent with that previously reported, with no new safety concerns. Grade 3/4 adverse events with at least 5% difference between BUP+FUL vs PBO+FUL, respectively, were increased alanine aminotransferase (25.7% vs 1.1%), increased aspartate aminotransferase (18.0% vs 2.8%), hyperglycemia (15.4% vs 0.2%) and rash (8.0% vs 0.0%). Conclusions: The BELLE-2 OS results showed a trend in favor of BUP+FUL, but did not meet statistical significance. More selective PI3K inhibition may improve treatment benefit and safety compared with pan-PI3K inhibition. Further assessment of the predictive benefit of ctDNA-confirmed PIK3CA mutations in this setting is required. Citation Format: Campone M, Im S-A, Iwata H, Clemons M, Ito Y, Awada A, Chia S, Jagiełło-Gruszfeld A, Pistilli B, Tseng L-M, Hurvitz S, Masuda N, Cortés J, De Laurentiis M, Arteaga CL, Jiang Z, Jonat W, Sellami D, El-Hashimy M, Le Mouhaër S, Sankaran B, Bourdeau L, Baselga J. Buparlisib (BUP) or placebo (PBO) plus fulvestrant (FUL) in postmenopausal patients (pts) with hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2–) advanced breast cancer (ABC): Overall survival (OS) results from BELLE-2, a randomized, phase III study [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr PD5-12.

Background In the NeoALTTO trial, the combination of trastuzumab and lapatinib for the neoadjuvant treatment of HER2 positive early breast cancer patients (pts) nearly doubled the rate of pathological complete response (pCR) compared with either anti-HER2 treatment alone. In the same trial, pCR was shown to be a surrogate for long-term outcome. Expression of ERBB2, ESR1 and immune signatures were the main drivers of pCR (Fumagalli et al. JAMA Oncol 2016). The main aim of the current study was to investigate the relevance of copy number aberrations (CNAs) for pCR and event-free survival (EFS). Methods For 271 out of the 455 pts enrolled in the study with sufficient tumour content, DNA was hybridized on CytoScan HD arrays. The log2 ratio intensities and B allele frequencies were segmented jointly using the multitrack segmentation algorithm. Integer level estimates of total copy number and major allele were obtained using GAP. Recurrent CNAs were found with GISTIC2. The genome instability index (GII) was defined as the median absolute deviation of the normalized copy number. Tumor infiltrating lymphocytes (TILs) and gene expression were obtained as described previously. The correlations between differents parameters were assessed using Spearman correlations (ρ). The Mann-Whitney test was used to relate binary and numerical features. EFS analysis was performed using the Cox proportional hazard model. Results CNAs estimates were obtained for 185 out of 271 pts. CNA distribution was similar to the ones observed in HER2+ pts from the METABRIC and the TCGA datasets. There were 64% of diploid pts, 26% of triploid and 9% of tetraploid or more. Aneuploidy level was not associated with pCR or EFS. Of interest, there were many significant differences in CNA profiles between ER+ and ER- pts. Those differences mirror those observed between ER+ and ER- among HER2- pts in TCGA (ρ=63%) and METABRIC (ρ=56%). ERBB2 amplification was predictive of high pCR (p=0.0007), albeit less so than ERBB2 expression, and ceased to be significant correcting for ERBB2 expression. The pCR rate increased with the GII (p=0.03), independently of ERBB2 amplification. The effect was stronger in ER+ patients (p=0.01). GISTIC analysis revealed 159 recurrent CNA regions. Amplification of 2 regions on 6q23-24 was significantly associated with higher pCR (p=0.00005 and p=0.00087, FDR=0.006 and 0.05). The most significant segment of 6q23-24 contained 39 genes, some whose expression level also predicted pCR (e.g. MAP3K5, p=10-4). Gene ontology analysis of the genes correlated with this segment highlighted the category 'response to interferon-alpha' (p=4.3x10-7). No amplified region or gene was found to be predictive of EFS, after multiple testing correction. Conclusions The amplification of ERBB2 was shown to be predictive of pCR, however its expression was more predictive. High genomic instability was associated with higher rate of pCR in ER+ subgroup. Of interest, a novel amplified region, involving chromosome 6 was shown to be predictive of pCR, which may warrant further investigation. Citation Format: Sotiriou C, Rothé F, Maetens M, Fumagalli D, Brown DN, Salgado R, Bradbury I, Pusztai L, Harbeck N, Ignatiadis M, Sarp S, de la Pena L, de Azambuja E, Huober J, Nuciforo P, Baselga J, Piccart M, Loi S, Venet D. Copy number aberration analysis to predict response to neoadjuvant anti-HER2 therapy: Results from the NeoALTTO phase III trial [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr GS1-04.

This abstract was withdrawn by the authors.

Background: Preclinical models suggest that in some HER2 overexpressed breast cancer cases, the extracellular domain of HER2, containing the binding region for trastuzumab (T) is not present due to proteolytic cleavage. Previous measurement of HER2 ECD and ICD in HeCOG 10/05 suggested that breast cancer cases that have low levels of ECD show decreased benefit from adjuvant T therapy (Carvajal et al, 2015). These cases may be more likely to show benefit from lapatinib(L), a small molecular tyrosine kinase inhibitor. NeoALTTO, an international multi-institutional trial comparing pre-surgical treatment with L vs T vs both, showed that pCR rates were around 25-30% for L or T but increased to 50% for both. This cohort allows us to test the hypothesis that patients with low ECD may benefit more from L than T. Methods: ECD and ICD were measured 382 cases using quantitative immunofluorescence (QIF) with domain specific antibodies (SP3, Spring biosciences for ECD and CB11, Biocare for ICD). Slides were stained and scanned, then measured using the AQUA method of QIF. All fields of view were scored and FOVs were averaged to generate a QIF score for each case. Index TMAs were used to standardize all autostainer runs and to define the QIF score cut-point that is equivalent to the clinical cut-point for the index TMA cases. Each case was then assigned to one of three groups; 1) High ECD and ICD, 2) Low ECD but High ICD, and 3) low ICD. Results: In the lapatinib arm, both group 1 and 2 showed a pCR rate of 25% (p>0.99), but in the trastuzumab arm, Group 1 pCR rate was 34% compared to 19% for group 2 (p=0.38). In the combination arm, group 1 showed a pCR rate of 59% compared to 29% for group 2 (p=0.046). In a logistic regression model for pCR, after adjustment for treatment arm and HR status the ECD/ICD status shows a significant predictive value (p = 0.002). Although this study is not powered for event free survival (EFS), at 6 years of follow up we found that patients in group 2 on the lapatinib arm show 92% EFS compared to 69% EFS in group 1 (p=0.17). The opposite trend is seen in both trastuzumab arms where EFS for group 1 on T showed 70% vs 62% for group 2 (p=0.57) and 77% vs 71% on the T+L arm (p=0.74). In a Cox regression model for EFS after adjustment for treatment arm and HR status, the ECD/ICD status is not significant (p=0.88) Conclusions: Cases with low levels of ECD compared to ICD appear benefit less than those with high levels of both ECD and ICD as assessed by pCR from treatments containing T. In contrast, those same patients also appear to benefit more, as assessed by EFS, on the L arm. These observations are consistent with the hypothesis that this assay could stratify benefit from L vs T based on the status of the ECD. Further assessment using this assay on the ALTTO cases is currently underway and may help confirm this observation. Citation Format: Rimm DL, Carvajal-Hausdorf D, Harbeck N, Fumagalli D, Rodrik-Outmezguine V, delaPena L, deAzambuja E, Huober J, Baselga J, Piccart M, Holmes E, Pusztai L. Low levels of HER2 extracellular domain (ECD) compared to intracelluar domain (ICD) in NeoALTTO may segregate benefit from lapatinib and trastuzumab in breast cancer [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P2-09-07.

Background: Everolimus (EVE) plus exemestane (EXE) doubled progression-free survival (PFS) while maintaining quality of life versus EXE alone in postmenopausal women with hormone receptor positive (HR+), HER2-negative metastatic breast cancer (mBC) (BOLERO-2 phase 3; NCT00863655). Pretreatment serum activin A was previously reported as a prognostic factor in first-line hormone therapy (letrozole vs tamoxifen) (Novartis P025) and anti-HER2 mBC (lapatinib vs trastzmab) (CCTG MA.31) trials. Here we investigate the prognostic and predictive ability of activin A in BOLERO-2. Methods: Activin A levels were determined on pretreatment serum samples using ELISA. Cox-proportional hazards model was used to assess the efficacy of EVE in the activin A low and high subgroups (median cut-point), and the prognostic effect of activin A on PFS and overall survival (OS). Results: Baseline activin A levels were determined in 513 patients (71% of 725 BOLERO-2 patients randomized 2:1 to EVE+EXE or EXE). Predictive and prognostic signals are shown in the table below Predictive and prognostic signalsPredictive/PrognosticEnd-pointAct-ivin ATreatmentNEventsMedian PFSHR (95% CI); p valuepredictivePFSHEXE93832.5 (1.5-2.8)-predictivePFSHEVE+EXE1631325.4 (4.1-6.8)0.46 (0.34 - 0.60); . In multivariate analysis (including sensitivity to prior hormone therapy and visceral disease), activin A remained a significant independent prognostic factor for PFS and OS [HR 0.57 (0.46-0.69) and 0.34 (0.27-0.43), respectively]. Conclusions: Higher serum activin A was strongly associated with shorter PFS and OS in HR+/HER2- mBC patients. Everolimus was efficacious regardless of serum activin A level. These results are similar to our previous studies in phase 3 trials of letrozole-tamoxifen (Novartis P025), and HER2-targeted therapy, lapatinib vs trastuzmab (CCTG MA.31): pretreatment serum activin A was prognostic for outcome, but was not a predictive factor for treatment arm selection. Citation Format: Ali SM, Chen D, Ali A, Krecko L, Leitzel K, Vasekar M, Nagabhairu V, Marks E, Polimera H, Richardson A, May M, He W, Patel P, Lavin M, Hofsess S, Sweetman R, Hortobagyi G, Baselga J, Lipton A. Serum activin A and outcomes in HR+ /HER2- metastatic breast cancer patients treated with everolimus: Results from BOLERO-2 [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P1-07-09.

BACKGROUND: As a neoadjuvant regimen for HER2-positive early breast cancer (BC), the use of two HER2-directed agents is more effective in producing pathological complete (pCR) responses than trastuzumab alone. Nevertheless, highly effective dual anti-HER2 combination may be unnecessary in patients who already benefit from a single agent. We previously reported that our 41-gene TRAR score is an accurate predictor of response to trastuzumab, with low scores being predictive of response to trastuzumab and favorable prognosis (Triulzi T. et al., 2015). PATIENTS AND METHODS: Tissue specimens from HER2-positive BC patients of Neo-ALTTO trial who received neoadjuvant trastuzumab and/or lapatinib plus paclitaxel were included in this study. Analysing RNA from fresh tissue using the 41-gene signature test, the area under the ROC curve (AUC) and the corresponding 95% confidence interval was computed to evaluate the predictive ability of TRAR score with respect to pCR, the primary endpoint of Neo-ALTTO. The prognostic role of TRAR score was investigated using a Cox regression model in univariate fashion. The patterns of Event Free Survival (EFS) according to the dichotomized TRAR score were estimated using the Kaplan–Meier method. RESULTS: The TRAR score was assessed for 226 of the 455 (49.7%) patients enrolled in the Neo-ALTTO study: 136 (60%) presented with T2 tumors, 188 (83%) with N0/1 and 128 (56.6%) with estrogen receptor negative BC. In details, basal TRAR score was available for 69, 79 and 78 patients assigned to neoadjuvant trastuzumab, lapatinib, and their combination, respectively. Overall, patients achieving a pCR showed significantly lower levels of TRAR score than those with residual disease (p CONCLUSION: Overall, we show that our 41-gene signature is accurate in predicting patient response to neoadjuvant HER2 targeted therapy in terms of pCR. In particular, low levels of TRAR score can identify a HER2-positive breast cancer subgroup highly responsive to trastuzumab as monotherapy for whom combination with other HER2-targeted drugs does not appear justified and may be one tool used for exploring de-escalating strategies without sacrificing outcomes. Citation Format: Di Cosimo S, Triulzi T, De Cecco L, Pizzamiglio S, de Azambuja E, Fumagalli D, Pusztai L, Harbeck N, Izquierdo M, de la Pena L, Huober J, Baselga J, Piccart M, Verderio P, Tagliabue E. Identifying clinically relevant subgroups of women with HER2-positive breast cancer: An analysis of Neo-ALTTO using the 41-gene TRAR score [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P2-09-03.

Background: Eribulin is the only cancer agent that has demonstrated a significant prolongation in overall survival on previously treated breast cancer patients. To date, no biomarker exists to prospectively select patients who will derive the maximum benefit from this chemotherapeutic. In the SOLTI1007-NeoEribulin study, we explored, in a prospective clinical trial, the efficacy and the association of pre-treatment expression of RNA in patients with HER2-negative breast cancer treated with neoadjuvant eribulin. Methods: SOLTI1007 is a phase II, open-label, single-arm, exploratory pharmacogenomic study of single agent eribulin as neoadjuvant treatment for stage I-II HER2-negative breast cancer (planned n=100 hormonal receptor-positive [HR+] and n=100 HR-negative). Patients received 1.4 mg/m2 of eribulin intravenously on Days 1 and 8 every 21-day cycle, for 4 cycles. Baseline and post-treatment (surgical) formalin-fixed, paraffin-embedded tissue samples were collected and gene expression profiled. PAM50 intrinsic subtype and the Risk of Relapse based on subtype and proliferation (ROR-P) were evaluated in each time-point. The association of each PAM50 signature and pathological complete response in the breast (pCRB) was evaluated using univariate logistic regression models. Results: Between September 2012 and October 2015, one hundred and seventy-four patients (TNBC n=73 and HR+ n=101) were recruited. Mean age (55.5), stage II (90%), negative axilla (78% and 67%), grade 3 (62% and 26%), mean tumor size (3 cm and 3.6 cm) and mean Ki-67 (61% and 31%). Completion of 4 cycles of eribulin was achieved by 85% of the patients. Grade 3-4 toxicities were observed in 19.54%, mostly due to neutropenia (5.1%) and alopecia (4.02%). The overall pCRB was 5.4%. No significant differences were observed between HR+ and TNBC disease. Distribution of the PAM50 intrinsic subtypes was as follows: Luminal A (n=43, 27.7%), Luminal B (n=42, 27.1%), Basal-like (n=63, 40.6%) and HER2-enriched (n=7, 4.5%). pCRB rates by subtype were the following: HER2-enriched (28.6%, 2/7), Luminal B (7.1%, 3/42), Basal-like (4.8%, 3/63), Luminal A (2.3%, 1/43). pCRB rates significantly (p=0.047) differed when HER2-enriched was compared to the other subtypes (odds ratio = 8.06, 95% CI 1.32-49.1). pCRB rate differed significantly by ROR-P (p=0.006): ROR-P high (17.1%, 6/35), ROR-P med (2.7%, 2/75), ROR-P low (2.2%, 1/45). Ki67 % by IHC did not predict pCRB (p=0.918). Subtype change at surgery occurred in 60% (3/5) HER2-enriched, 44.1% (15/34) of Luminal Bs, 10.3% (4/39) of Luminal A and 5.4% (2/37) of Basal-like tumors. 100% of subtype changes in Luminal B disease were to Luminal A. Conclusions: From a response and biological perspective, patients with HER2-enriched and Luminal B disease may benefit the most from eribulin therapy. Mechanistically, our gene expression data further supports previous preclinical evidence suggesting that eribulin triggers a phenotypic conversion. Citation Format: Prat A, Ortega V, Villagrasa P, Paré L, Galván P, Oliveira M, Nucíforo P, Lluch A, Morales S, Amillano K, Lopez R, Gonzalez R, Manso L, Martinez J, Llombart A, De la Peña L, Di Cosimo S, Rubio IT, Harbeck N, Baselga J, Cortés J. Efficacy and gene expression results from SOLTI1007 NEOERIBULIN phase II clinical trial in HER2-negative early breast cancer [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P1-09-09.

Background: The combination of taxanes with trastuzumab (H) and pertuzumab (P) for first line treatment of HER2-positive metastatic breast cancer (MBC) is associated with improved progression-free survival (PFS) and overall survival (OS). Treatment per physician's choice with anti-HER2 therapy after second line therapy is associated with a median PFS of 3 months. While continued use of H in therapeutic combinations after progression on H-based therapy is common, the efficacy of continuing HP-based treatment after progression on P-based therapy is unknown. Methods: This is a single arm phase II trial of gemcitabine (G) with HP. Eligible patients had HER2-positive (IHC 3+ or FISH ≥ 2.0) MBC with prior HP-based treatment and ≤ 3 prior chemotherapies. Patients received G (1200 mg/m2) on days 1 and 8 of a q 3 week (w) cycle, and H (8 mg/kg load → 6 mg/kg) and P (840 mg load → 420 mg) q3w. The primary endpoint is PFS at 3 months. Secondary endpoints include OS, safety and tolerability. An exploratory endpoint is to compare PFS by RECIST criteria versus 18-F FDG-PET response criteria. Using a Simon optimal 2-stage design, 21 patients were enrolled in stage 1. The successful 3-month PFS rate for stage 1 was set at 57% to allow accrual to stage 2 for a total of 45 patients. The study therapy will be considered successful if at least 27/45 (60%) patients are progression free at 3 months. Results: As of June 9, 2016, 28 patients are enrolled; 21 are evaluable at 3 months and 7 have not had 3-month evaluation. At 3 months, 16/21 (76%) are progression free; 5 patients have progressed. The 3 month-PFS results for evaluable patients will be updated. There are no cardiac or febrile neutropenic events to date. Initially, 5 of 22 (23%) patients required G dose reduction (4 due to grade 3 neutropenia and 1 due to grade 3 vomiting) and the study was amended to lower initial G dose to 1000 mg/m2. Conclusions: The preliminary 3 month-PFS is 76% (95% CI 55% to 89%) in evaluable patients, and updated data will be presented. These findings suggest clinical benefit when P is continued beyond progression. Citation Format: Iyengar NM, Smyth L, Lake D, Gucalp A, Singh JC, Traina TA, DeFusco P, Dickler MN, Fornier MN, Goldfarb S, Jhaveri K, Modi S, Troso-Sandoval T, Argolo D, Jack K, Ulaner G, Jochelson M, Baselga J, Norton L, Hudis CA, Dang CT. Phase II study of gemcitabine, trastuzumab, and pertuzumab for HER2-Positive metastatic breast cancer after prior pertuzumab-based therapy [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P4-21-34.

Background: Somatic mutations in ERBB2 are a new class of oncogenic drivers in HER2–non amplified MBC. Neratinib is an irreversible pan-HER tyrosine kinase inhibitor that inhibits the growth of ERBB2-mutant breast tumors in preclinical models and has encouraging single-agent clinical activity in patients (pts) with ERBB2-mutant, HER2–non amplified MBC. Bi-directional signaling between HER2 and ER may limit the effectiveness of endocrine and HER2 directed therapy, if each is given alone, in ER+ MBC with ERBB2 amplifications/mutations. Preclinical data suggest that dual blockade of ER and HER2 signaling results in enhanced anti-tumor activity in ER+ HER2+ MBC. SUMMIT, a multicenter multi-histology phase II 'basket' trial, is investigating the efficacy of neratinib monotherapy (in ER+ and ER– pts) and neratinib + fulvestrant (ER+ pts only) in ERBB2-mutant MBC. Methods: MBC pts with ERBB2 mutations documented by local testing were eligible and received oral neratinib 240 mg qd. Pts with ER+ MBC received fulvestrant 500 mg, a selective ER degrader, in addition to neratinib on d1 & 15 of month 1 then on d1 q4w. Patients received high dose loperamide prophylaxis during cycle 1. Primary endpoint is objective response rate (ORR) at 8w, defined using RECIST 1.1 and/or modified PERCIST assessments. Secondary endpoints include ORR, clinical benefit rate (CBR), progression free survival (PFS), and safety. Mutation profiling and central confirmation of ERBB2 mutation(s) from available fresh or archival tumor tissues and plasma DNA were performed retrospectively by next-generation sequencing (MSK-IMPACT). Clinicaltrials.gov: NCT01953926. Results: As of 23 Sep 2016, 35 efficacy-evaluable ERBB2-mutant MBC pts received neratinib, either as monotherapy (n=24) or in combination with fulvestrant (n=11). Efficacy findings are shown in the table. The overall safety profile of neratinib + fulvestrant was similar to that previously reported with neratinib monotherapy. Grade 3 diarrhea rate was 24% with neratinib monotherapy and 18% with neratinib + fulvestrant. Neratinib monotherapyNeratinib + fulvestrant(n=24)(n=11)Best Overall Response (confirmed and unconfirmed), n (%)8 (33.3)6 (54.5)[95% CI][15.6–55.3][23.4–83.3]CR3 (12.5)2 (18.2)PR5 (20.8)4 (36.4)aORR at 8 weeks, n (%)8 (33.3)5 (45.5)[95% CI][15.6–55.3][16.7–76.6]CR2 (8.3)2 (18.2)PR6 (25.0)3 (27.3)ORR confirmed, n (%)5 (20.8)2 (18.2)b[95% CI][7.1–42.2][2.3–51.8]CR3 (12.5)1 (9.1)PR2 (8.3)1 (9.1)CBR, n (%)10 (41.7)6 (54.5)[95% CI][22.1–63.4][23.4–83.3]CR, complete response; PR, partial response.aThere was 1 pt with PR at week 16; bAt time of data cut-off 4 pts are still on treatment. Conclusions: Encouraging clinical activity has been observed with neratinib + fulvestrant in heavily pretreated pts with ERBB2-mutant, ER+ MBC. Clinical efficacy in the ER+ MBC cohort met pre-specified efficacy requirements; a confirmatory trial of neratinib + fulvestrant for targeting ERBB2 mutations in ER+ MBC is warranted. The safety profile of neratinib was acceptable and diarrhea was manageable with loperamide prophylaxis. Citation Format: Hyman D, Piha-Paul S, Saura C, Arteaga C, Mayer I, Shapiro G, Loi S, Lalani A, Xu F, Cutler R, Butturini A, Bryce R, Meric-Bernstam F, Baselga J, Solit D. Neratinib + fulvestrant in ERBB2-mutant, HER2–non-amplified, estrogen receptor (ER)-positive, metastatic breast cancer (MBC): Preliminary analysis from the phase II SUMMIT trial [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr PD2-08.

Background:Anti-HER2 agents are associated with an increased risk of cardiotoxicity, occurring mostly during treatment and being generally reversible. To date, no cardiac biomarkers have been validated as predictive markers of cardiotoxicity in patients (pts) receiving anti-HER2 therapies. We evaluated high sensitivity (HS) troponin T (TnT) and N-terminal pro-brain natriuretic peptide (NT-proBNP) in pts treated with neoadjuvant anti-HER2 therapies to evaluate if early elevation of cardiac biomarkers predicts early or late cardiac events. Material and Methods: 455 pts were randomized to receive either lapatinib (154 pts), trastuzumab weekly (149 pts), or lapatinib with trastuzumab for a total of 6 weeks (152 pts). After this biological window, pts continued on the same targeted therapy plus 12-weekly paclitaxel until definitive surgery. After surgery, patients received adjuvant FEC (3x) followed by the same HER2 therapy as in the neoadjuvant phase for further 34 weeks (to complete 52 weeks in total). Eligible pts had an LVEF ≥50%. Cardiac biomarkers were centrally tested in plasma samples collected at baseline, week 2 (W2) and at surgery. Elevated biomarker was defined as either TNT >0.015 μg/L or NT-proBNP >125 pg/mL. The small number of pts and rarity of marker elevations allowed only descriptive analyses. Results: At a median follow-up of 3.8 years, 280 pts had cardiac biomarkers tested at baseline (61.5%) and NT-proBNP was elevated in 39 pts (13.9%) while TNT was elevated in only 1 pt (0.35%). From those 39 pts with NT-proBNP elevated at baseline, only 1 pt experienced a cardiac event. Also, hypertension was presented in 14 pts (24.5%) with elevated NT-proBNP. Serial measurements were available in 173 pts (61.7%) and NT-proBNP was elevated in 25, 10 and 21 pts at baseline, W2 and at surgery, respectively, while among 171 pts (61%) TNT was elevated in 1, 1 and 5 pts, respectively. There were 13 cardiac events in 11 pts in the entire trial. Five of these pts had a measurement of cardiac biomarkers at baseline (non-elevated NT-prBNP and TNT were observed in 4 and 5 pts), 9 of them had a measurement at week 2 (non-elevated NT-prBNP and TNT were observed in 8 and 9 pts) and 3 of them at surgery (non-elevated NT-prBNP and TNT were observed in 3 and 3 pts), respectively. The following table show the low specificity of the cardiac biomarkers. Patients without cardiac event (N)Patients with cardiac event (N)Patients with elevated markerElevated NT-proBNP Baseline38139Week 229130Surgery40040Elevated TNT Baseline101Week 2101Surgery606 During adjuvant phase, 13 pts experienced LVEF drop to Conclusions: Despite the small sample size, we demonstrated that cardiac biomarkers are rarely elevated in pts receiving anti-HER2 therapies, which is probably due to the absence of myocyte necrosis with respect to TNT, and the lack of chamber dilation in the case of NT-proBNP after exposure to these drugs. In addition, few cardiac events were present in this population not previously exposed to anthracycline-based chemotherapy; therefore the use of cardiac biomarkers in this population may be unnecessary. Citation Format: de Azambuja E, Bradbury I, Ewer M, Campbell C, Zardavas D, Ameels H, Baselga J, Huober J, Izquierdo M, Bozovic-Spasojevic I, Maetens M, Harbeck N, Pusztai L, Piccart M, Rodeheffer R, Sutter T. Cardiac biomarkers for early detection and prediction of trastuzumab and/or lapatinib-induced cardiotoxicity in patients with HER2 positive early breast cancer (BIG 1-06) [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P4-21-09.

Background: The phosphatidylinositol 3-kinase (PI3K) pathway is frequently dysregulated in hormone receptor (HR)-positive breast cancer (BC), with activating mutations of PIK3CA detected in ~35–45% of patients (pts). Acquired mutations in the ESR1 gene, which encodes estrogen receptor α, may be associated with resistance to aromatase inhibitor (AI) therapy. Taselisib is a potent and selective PI3K inhibitor, with greater selectivity against mutant PI3Kα isoforms than wild-type (WT) via a unique mechanism. In phase I studies, taselisib plus fulvestrant had clinical activity and manageable tolerability in pts with HR-positive BC. We report exploratory analyses of PIK3CA and ESR1 from circulating tumor DNA (ctDNA). Methods: In this phase II, open-label, single-arm study (PMT4979g; NCT01296555), pts were postmenopausal with HER2-negative, HR-positive locally advanced or metastatic BC and progression or non-response to ≥1 prior endocrine therapy in the adjuvant or metastatic setting. Pts received taselisib (6 mg capsule orally, daily) plus fulvestrant (500 mg intramuscular on Days 1 and 15 of Cycle 1, then Day 1 of each 28-day cycle) until disease progression or unacceptable toxicity. PIK3CA-mutation testing on archival tumor tissue used the cobas® PIK3CA Mutation Test. The Sysmex Inostics' BEAMing Digital PCR platform was used for ctDNA analysis of ESR1 and PIK3CA mutations (pre-dose on Cycle 1, Day 1). Primary endpoints were objective response rate (ORR) and clinical benefit rate (CBR) in all pts and those with PIK3CA mutations. ORR was confirmed complete response (cCR) and confirmed partial response (cPR). CBR was cCR, cPR, or stable disease for ≥6 months. Secondary endpoints included safety, efficacy, pharmacokinetics, and exploratory biomarker analysis. Results: 60 pts were enrolled. Median age was 61.5 years (range 31–82). In the metastatic setting, pts had received prior chemotherapy (21.7%) and prior hormonal therapy (50.0%). 86.7% of pts had received prior treatment with an AI. 45 pts had PIK3CA mutation status from archival tumor tissue and ctDNA testing; concordance was 86.7% (39/45). ctDNA analysis, vs archival tumor tissue testing, identified 4 pts and 9 pts with PIK3CA mutations from pts with WT and unknown PIK3CA mutation status, respectively. Based on ctDNA analysis (N=60), 13 pts (21.7%) had mutations in both ESR1 and PIK3CA, 21 pts (35.0%) were 'mutation not detected' (MND) for both genes, 8 (13.3%) had ESR1 mutations and PIK3CA MND, and 18 (30.0%) had ESR1 MND and PIK3CA mutations. In pts with measurable disease at baseline, confirmed responses (all partial) were: PIK3CA mutation, 38.1% (8/21); PIK3CA MND, 8.7% (2/23); all pts, 22.7% (10/44). CBRs were: PIK3CA mutation, 42.9%; PIK3CA MND, 17.4%; all pts, 29.5%. ORR and CBR from ctDNA analyses were similar to archival tumor tissue data. Conclusions: ctDNA analysis identified PIK3CA mutations in pts with previously unknown or WT mutation status from archival tumor tissue; ORR and CBR were similar to those from archival tumor tissue suggesting that PIK3CA mutation testing from ctDNA may be used as a surrogate when tissue is unavailable. 21.7% of pts had mutations in both ESR1 and PIK3CA. Citation Format: Dickler MN, Saura C, Oliveira M, Richards DA, Krop IE, Cervantes A, Stout TJ, Jin H, Savage HM, Wilson TR, Baselga J. Phase II study of taselisib (GDC-0032) plus fulvestrant in HER2-negative, hormone receptor-positive advanced breast cancer: Analysis by PIK3CA and ESR1 mutation status from circulating tumor DNA [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P6-12-01.

Background: Eribulin is a non-taxane, microtubule dynamics inhibitor approved for the treatment of patients with locally advanced or metastatic breast cancer. To date, no biomarker exists to prospectively select patients who will derive the maximum benefit from this chemotherapeutic. In this study, we explored, in a prospective clinical trial, the efficacy and the association of pre-treatment expression of mRNA with response in patients with HER2-negative breast cancer treated with neoadjuvant eribulin. Results of the HR+ cohort are presented here. Methods: SOLTI1007 is a phase II, open-label, single-arm, exploratory pharmacogenomic study of single agent eribulin as neoadjuvant treatment for stage I-II HER2-negative breast cancer (n=100 HR+ and n=100 HR-negative). Patients received 1.4 mg/m2 of eribulin mesilate intravenously on Days 1 and 8 every 21-day cycle, for 4 cycles. Baseline, C2D1, and post-treatment (surgical) formalin-fixed, paraffin-embedded tissue samples were collected and gene expression profiled. The PAM50 genes and 492 additional breast cancer-related genes were evaluated using the nCounter platform. Research-based intrinsic subtype and the Risk of Relapse based on subtype and proliferation (ROR-P) were evaluated using the Parker et al. JCO 2009 algorithm. The association of each signature and pathological complete response in the breast (pCRb) was evaluated using univariate logistic regression models. Genes found differentially expressed between screening and surgical specimens were identified using a paired two-class Significance Analysis of Microarrays. Results: 92 evaluable patients were included. Mean age: 55.7. Mean tumor size: 3.7 cm. Mean Ki-67 %: 30.3. The overall pCRb rate was 5.4%. Distribution of the intrinsic subtypes was as follows: Luminal A (n=36, 39.1%), Luminal B (n=34, 37.0%), Basal-like (n=10, 10.9%), Normal-like (n=10, 10.9%) and HER2-enriched (n=2, 2.2%). pCRb rates differed significantly by subtype (p=0.009): Luminal B (11.7%, 4/34), HER2-enriched (50%, 1/2), Luminal A (0%, 0/36), Basal-like (0%, 0/10), Normal-like (0%, 0/10). pCRb rate differed significantly by ROR-P (p=0.018): ROR-P high (16.7%, 4/24), ROR-P med (1.9%, 1/52), ROR-P low (0%, 0/16). Ki67 % did not predict pCRb (p=0.406). Subtype change at surgery occurred in 48.3% (14/29) of Luminal Bs, 13.8% (4/29) of Luminal As, 100% (2/2) of HER2-enriched and 12.5% (1/8) of Basal-like tumors. 78.6% (11/14) of subtype changes in Luminal B disease were to Luminal A. Compared to screening biopsies, 136- and 141- genes were found up- and down-regulated in surgical specimens (False Discovery Rate Conclusions: From a response and biological perspective (i.e. induction of a Luminal A phenotype), patients with Luminal B disease might benefit the most from eribulin therapy. Strategies combining eribulin with endocrine therapy seem warranted in Luminal B breast cancer. Citation Format: Prat A, Ortega V, Paré L, Galván P, Oliveira M, Nucíforo P, Lluch A, Morales S, Amillano K, Lopez R, González R, Manso L, Martínez J, Llombart A, de la Peña L, di Cosimo S, Rubio IT, Harbeck N, Baselga J, Cortés J. Efficacy and gene expression results from eribulin SOLTI1007 neoadjuvant study. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P3-07-66.

Background: The PI3K/Akt/mTOR pathway is frequently activated in breast cancer (BC) and is important for the oncogenic function of HER2. Buparlisib is an oral pan-PI3K inhibitor that targets all 4 isoforms of class I PI3K (a, b, g, d). Clinical activity was observed with buparlisib in patients (pts) with advanced BC as a single agent, and in combination with endocrine and anti-HER2 treatment. Methods: NeoPHOEBE (NCT01816594) is a phase II, randomized, double-blind, parallel-cohort study of neoadjuvant buparlisib/placebo plus trastuzumab and weekly paclitaxel in women with, untreated primary HER2-positive BC. Pts were stratified upfront into 2 independent cohorts according to PIK3CA mutation status. Other eligibility criteria: tumor size >2 cm; unilateral disease; available tumor tissue for central review of estrogen receptor (ER), HER2 status, and PIK3CA genotype; known PIK3CA mutation status; and ECOG PS ≤1. Pts in each cohort (PIK3CA mutant or wild-type [wt]) were randomized (1:1) to receive continuous daily buparlisib (100 mg) or placebo and weekly trastuzumab (4 mg/kg loading dose then 2 mg/kg) for 6 weeks, followed by continuous daily buparlisib (80 mg) or placebo with weekly trastuzumab (2 mg/kg) and weekly paclitaxel (80 mg/m2) for 12 weeks. Study treatment was followed by surgery. Stratification at randomization was based on PIK3CA (mutant vs wt) and ER (positive vs negative) status. The primary endpoint was pathologic complete response (pCR; ypT0) rate at time of surgery. The key secondary endpoint was objective response rate (ORR) at the end of week 6. Other secondary endpoints included pCR by other definitions, ORR prior to surgery, pCR and objective response by ER status, percent of pts with node-negative disease at surgery, rate of breast conserving surgery, and safety, as well as pCR by PTEN expression, Ki67 level, apoptosis rates, percentage of tumor infiltrating lymphocytes (TIL), and by phenotype of 50% TIL at baseline. The sample size is based on a minimax 2-stage randomized phase II design with a prospective control. This design allowed for early stopping if the desired efficacy was not observed after stage 1. Both cohorts were powered (80%) to detect a clinically meaningful increase in pCR of 18% at a one-sided significance level (α=0.15). Results: Between 9/2013 and 10/2014 50 pts were randomized in 38 sites in 4 countries. Recruitment was suspended due to toxicity in 10/2014. Median age was 50 years, 42 pts had a PIK3CA wt and 8 a PIK3CA mutant tumor, 62% of pts presented with HER2+/ER+, 90% with ductal or ductal-lobular invasive, and 62% with G3 tumors; 86% had Ki67 >20%; 9 pts reported a serious adverse event including 3 pts with hepatotoxicity. Overall 14/50 (28 %) pts developed grade 3-4 liver enzyme elevation, of whom 9 (64%) recovered to at least grade1. Final safety and efficacy data on the primary endpoint (pCR) and biomarker data will be presented at the meeting. Conclusions: The NeoPHOEBE study investigates for the first time the efficacy of adding a pan-PIK3 inhibitor to a taxane/trastuzumab-based neoadjuvant therapy in pts with primary HER2-positive BC with or without a PIK3CA mutation. Citation Format: Loibl S, de la Pena L, Nekljudova V, Zardavas D, Michiels S, Denkert C, Rezai M, Bermejo B, Lee S-C, Turri S, Urban P, Kümmel S, Lux M, Piccart M, von Minckwitz G, Baselga J, Loi S. Phase II, randomized, parallel-cohort study of neoadjuvant buparlisib (BKM120) in combination with trastuzumab and paclitaxel in women with HER2-positive, PIK3CA mutant and PIK3CA wild-type primary breast cancer – NeoPHOEBE. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P1-14-01.

Background: PARP1/2 inhibitors (PARPi) are active anti-cancer agents in BRCA1 or BRCA2 mutation carriers (BRCA) with advanced breast or ovarian cancer. However, not all BRCA-tumors respond to PARP blockade, and eventually all develop acquired resistance. Little is known about clinically relevant mechanisms of PARPi resistance in BRCA-breast cancer. Here, we sought to identify biomarkers correlating with primary and acquired resistance to PARPi using PDX derived from both the early disease and the metastatic setting. Methods: We have developed a panel of PDX from patients harboring germline BRCA1 or BRCA2 mutations, namely from 12 primary and advanced breast cancer and 1 high-grade serous metastatic ovarian cancer (HGSOC). The antitumor activity of the PARP1/2 inhibitor olaparib as single agent (50 mg/kg) was assessed in all models. To study the mechanisms of acquired resistance, the olaparib-sensitive PDXs were exposed to olaparib for >100 days, until individual tumors regrew. The tumor's capacity to repair DNA double strand breaks was estimated by quantification of the BRCA1 and RAD51 nuclear foci in the S-phase of the cell cycle. We investigated the correlation between the tumor's BRCA1/RAD51 foci formation and sensitivity to olaparib, and also identified potential genetic modifiers of PARPi sensitivity by targeted sequencing. Results: Four out of 13 PDX (31%) treated with single agent olaparib exhibited tumor regression or disease stabilization. Nuclear BRCA1/RAD51 foci formation correlated with PARPi resistance in six BRCA1 PDX models investigated, either with primary or acquired resistance. No reversions in BRCA1/2 mutations were identified as the mechanism of olaparib resistance. We identified four potential genetic modifiers of PARPi sensitivity and the corresponding validating studies will be presented. Conclusions: Among our BRCA PDX, reactivation of HR functionality is a frequent event that is associated with PARPi resistance and seems to occur through mechanisms other than secondary mutations in BRCA1/2 in contrast to what it has been reported for HGSOC. Citation Format: Cruz C, Bustos Ld, Gris A, Palafox M, Castroviejo M, Llop A, Morancho B, Diez O, Gutiérrez S, Caratú G, Prudkin L, Bruna A, Caldas C, O'Connor MJ, Rubio IT, Arribas J, Baselga J, Cortes J, Serra V, Balmaña J. PARP inhibition in breast and ovarian patient-derived tumor xenografts (PDX) harboring germline BRCA1/2 mutations unveils mechanisms of primary and acquired resistance that restore homologous recombination (HR). [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P4-07-05.

Introduction T-DM1 is indicated for the treatment of advanced HER2-positive MBC in patients who previously received trastuzumab and a taxane (separately or in combination) based on data from the phase 3 EMILIA study (BO21977/TDM4370g; NCT00829166). In the primary PFS and second interim OS analyses, respectively, T-DM1 significantly improved PFS (median 9.6 vs 6.4 months; HR=0.65; 95% CI, 0.55–0.77; p Methods EMILIA was a randomized, open-label study of patients with centrally confirmed HER2-positive (IHC3+ and/or FISH amplification ratio ≥2.0), unresectable, locally advanced or MBC, previously treated with trastuzumab and a taxane. Patients were randomized 1:1 to T-DM1 (3.6 mg/kg IV every 3 weeks) or X (1000 mg/m2 PO twice daily, days 1–14 every 3 weeks) plus L (1250 mg PO daily). The final OS analysis was to be conducted following 632 events, and these results are descriptive only. Since the OS efficacy boundary (HR Results From Feb 2009 to Oct 2011, 991 patients were randomized to T-DM1 (n=495) or XL (n=496). Patient disposition by the data cutoff (31 Dec 2014) is shown in Table 1. OS was longer with T-DM1 vs XL (median OS 29.9 vs 25.9 months; HR=0.75; 95% CI, 0.64–0.88; p=0.0003). In a sensitivity analysis, which censored crossover patients at the time of switching from XL to T-DM1, the HR was 0.69 (95% CI, 0.59–0.82; p Table 1. Patient disposition. T-DM1 (n=495)XL (n=496)Median treatment duration, months7.6X: 5.3 L: 5.5Median duration of follow-up, months47.841.9Discontinued study, n (%)364 (74)404 (82)Crossover, n (%) Per protocolaNot applicable136 (27)Non-protocol therapybX: 252 (54)X: 53 (11) L: 224 (48)L: 74 (15)aMedian duration of follow-up among per-protocol crossover patients was 24.1 months.bBy investigator choice after study treatment discontinuation; X or L could be given in combination with each other or other agents after progression. Table 2. Safety summary in patients who received ≥1 dose of study treatment.n (%)T-DM1 (n=490)XL (n=488)Grade ≥3 AEs233 (47.6)291 (59.6)Serious AEs91 (18.6)99 (20.3)AEs leading to dose reduction91 (18.6)X: 205 (42.0) L: 98 (20.1) Conclusions This final analysis of EMILIA shows an OS benefit of T-DM1 compared with XL. While median drug exposure was longer with T-DM1 than XL, T-DM1 was associated with fewer grade ≥3 AEs and AEs leading to dose reduction compared with XL. These final OS results confirm that T-DM1 treatment improved survival, even in the presence of treatment crossover, and reaffirm T-DM1 as the standard of care in patients with previously treated HER2-positive MBC. Citation Format: Diéras V, Miles D, Verma S, Pegram M, Welslau M, Baselga J, Krop I, Blackwell K, Kang B, Xu J, Green M, Gianni L. Trastuzumab emtansine improves overall survival versus capecitabine plus lapatinib in patients with previously treated HER2-positive advanced breast cancer: Final results from the phase 3 EMILIA study. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P4-14-01.

Background: Trastuzumab and pertuzumab (HP) with standard chemotherapy is approved for use in the neoadjuvant setting. We performed a retrospective analysis of patients (pts) treated with dose-dense doxorubicin and cyclophosphamide (AC) → paclitaxel, trastuzumab, pertuzumab (THP) in the neoadjuvant setting. Here we report the pathologic complete response (pCR) rate. Methods: We abstracted medical records of patients who were treated with pertuzumab-based therapy in the neoadjuvant setting from September 1, 2013 to March 1, 2015. Charts were analyzed for pt demographics, stage of breast cancer, pathology reports, surgical data, and information on systemic therapy. Results: Charts from 66 pts were reviewed; 60 pts were evaluable for pCR defined as absence of invasive disease in the breast, and 6 were not (3-no anthracycline, 1-incomplete chart, 1-no surgery yet, 1-metastatic). Median age was 47 years (range 28-68 years). Of 60 pts, 52 (86%) had operable breast cancer (T1-3, N0-1, M0) of which 7 had clinical stage I disease (T1N0)]; 7 (12%) had locally advanced disease (T2-3, N2-3, M0 or T4a-c, any N, M0), and 1 (2%) had inflammatory breast cancer (T4d, any N, M0). 49 (82%) and 11 (18%) had hormone receptor (HR)-positive and negative diseases, respectively. All patients had HER2-positive breast cancer defined as immunohistochemistry (IHC) 3+ and/or fluorescent in-situ hybridization (FISH) of > 2.0. 30 pts (50%) underwent mastectomy and lumpectomy, respectively. Out of 60 evaluable pts, 41 (68%) had pCR; 32/49 (65%) with HR-positive and 9/11 (82%) with HR-negative diseases had pCR, respectively. Overall 58/60 (97%) pts completed neoadjuvant therapy; 2 did not (1 developed Steven Johnson Syndrome after one cycle of AC and 1 developed pneumonitis after third weekly dose of T with HP). Conclusions: At our single center experience the pCR rate of dose dense AC→THP is high at 68 %. These data are similar to results seen in the TRYPHAENA study, and we await the results from the BERENICE trial evaluating pCR as a secondary endpoint. Patient Demographics Age, years 5516 (26%) ECOG Performace Status 031 (52%)129 (48%) Hormone receptor (HR) status HR+ Her2+49 (82%)HR- Her2+11 (18%) Status of Her-2 Positivity IHC positive52 (86%)FISH positive8 (14%) Median tumor size2.6cm (range: 1-8.4cm) Stage Operable (T1-2, N0-1, M0)52 (86%)Operable Stage I7 (12%)Operable Stage II/III45 (74%)Locally advanced (T2-3, N2-3, M0 or T4a-c, any N, M0))7 (12%)Inflammatory (T4d, any N, M0)1 (2%) Type of surgery Lumpectomy30 (50%)Mastectomy30 (50%) Citation Format: Singh JC, Sugarman S, Jones L, Boafo C, Patil S, Schweber S, Yu A, Argolo D, Modi S, Iyengar N, Smyth L, Norton L, Baselga J, Hudis C, Dang C. Pathologic complete response rate with doxorubicin and cyclophosphamide followed by weekly paclitaxel with trastuzumab and pertuzumab in patients with HER2-positive early stage breast cancer: A single institution experience. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P1-14-17.

Background: Dual anti-HER2 blockade with trastuzumab and pertuzumab (HP) plus chemotherapy is an effective therapy (Rx) in the 1st-line setting for HER2-positive metastatic breast cancer (MBC). Our single arm phase II study included patients (pts) treated with HP plus paclitaxel in the 2nd-line setting with progression-free survival (PFS) benefit. Recently, we reported results from a retrospective study of pts treated at our institution, suggesting a longer PFS for those who received HP-based Rxs when compared to any other anti-HER2 based Rxs in the 2nd-line setting. To further assess the activity of this combination in later Rx lines, we conducted a retrospective analysis of pts with HER2-positive MBC who had progressive disease after 2nd-line and were treated with HP-based Rxs in the 3rd and later lines at MSKCC. Historically, the median (med) PFS in this setting with trastuzumab-based Rx is about 3-4 months. Methods: Pts diagnosed with HER2-positive MBC and treated with HP-based Rxs at MSKCC between 1-1-2011 and 03-30-2015 and who progressed on 2nd-line Rx were identified through an institutional database. Primary endpoint was PFS in 3rd and later treatment lines. Results: 70 pts who received any HP-based Rx in the 3rd or later lines of treatment were eligible. The med number of prior anti-HER2 Rx was 3. The baseline characteristics and Rxs are summarized in Table 1. The med PFS for the entire cohort was 5.7 months (95% CI, 4.8-6.5). Conclusions: In this retrospective analysis involving heavly pretreated patients, HP-based Rx appears to be an active regimen and compares favorably to historical data. This supports the NCCN endorsement of HP-based Rx in later lines if HP has not been delivered previously. Baseline Characteristics and treatments (n=70)Characteristic(n)(%)Age Median56 Range27-83 Gender Female70100.0Male00.0Race Black1014.3White5477.1Other68.6Ethnicity Non Hispanic6694.3Hispanic45.7ER/PR status ER and PR negative2738.6ER and/or PR positive4361.4Type of disease Non visceral1622.9Visceral5477.1Visceral CNS2130.0Anti-HER2 in early stage Yes2941.4No4158.6Line of therapy 3rd line1927.14th line1521.45th line912.96th line912.97th line811.48th line and beyond1014.3HP-based regimens Chemotherapy + HP5477.1Endocrine therapy + HP57.1HP alone912.9Other22.9 Citation Format: Argolo D, Friedman M, Smyth L, Iyengar N, Singh J, Patil S, Norton L, Baselga J, Hudis C, Dang C. Activity of HP-based therapies as third and later lines for the treatment of HER2-positive metastatic breast cancer: A retrospective study from a single institution. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P4-13-20.

Background: The Y537S and D538G mutations in ESR1 are recurrent alterations in metastatic breast cancer (MBC) that promote ligand-independent receptor activation and resistance to estrogen deprivation therapy in laboratory models. The clinical prevalence of these mutations is not well established, but has been reported to be ∼10% by tumor sequencing. Cell free DNA (cfDNA) analysis typically reflects tumor-derived genetic alterations and can be used to characterize a population of patients at a common time point. We hypothesized that cfDNA could be used to detect ESR1 mutation at entry and its clinical impact in a large subset from BOLERO-2 that randomized patients with MBC to Exemestane (EXE) or EXE plus Everolimus (EVE). Methods: Patients with ER+/HER2– MBC with prior exposure to at least 1 non-steroidal aromatase inhibitor (NSAI) were enrolled in BOLERO-2. cfDNA was extracted from 560 baseline plasma samples using QIAamp Circulating DNA kit or QIAsymphony DSP Virus/Pathogen kit. Samples were analyzed by droplet digital PCR for Y537S and D538G. Cox-proportional hazards model was used to assess progression free survival (PFS) in patient subgroups defined by each ESR1 mutation, and the prognostic effect of each ESR1 mutation on overall survival (OS). Results: Of 541 evaluable patients (74.7% of study population), 156 (28.8%) had mutation in ESR1 in D538G (21.1%) and/or Y537S (13.3%) with 30 samples having both mutations. Sequencing of 302 archival tumor specimens (244 primary and 57 metastases) from this study only yielded 4 instances of D538G (1.3%) and 1 Y537S (0.3%). In the overall population, both mutations were poor prognostic factors associated with shorter OS (Table 1). Table 1AlterationNEventsMedian OS (95%CI)HR (95%CI)WT38521732.1 (28.1-36.4) D538G835726.0 (19.2-32.4)1.25 (1.02-1.54)Y537S423020.0 (13.0-29.3)2.31 (1.34-3.97)Double mt302415.2 (10.9-27.4)1.77 (1.31-2.39) PFS results were different for the two mutations. D538G but not Y537S mutation was associated with a shorter PFS with EXE compared to wild type (WT), (hazard ratios, D538G: 1.44 [95%CIs, 1.04-1.99] and Y537S: 0.92 [95%CIs, 0.44-1.93]). The D538G mutant group derived a similar benefit as WT from the addition of EVE to EXE, whereas the Y537S group did not (Table 2). Table 2AlterationGroupNEventsMedian PFS (95%CI)HR (95%CI)WTEXE1281163.9 (2.8-4.2)0.4 (0.31-0.51) EXE/EVE2571728.5 (6.9-9.9) D538GEXE24222.7 (1.4-2.8)0.34 (0.2-0.57) EXE/EVE59455.8 (4.2-8.4) Y537SEXE21164.1 (1.4-6.7)0.98 (0.49-1.94) EXE/EVE21194.2 (1.4-5.4) Conclusions: cfDNA analysis identifies a high rate of the Y537S and D538G ESR1 mutations in ER+ NSAI-treated MBC. As the two mutations may only represent 50-60% of all activating ESR1 mutations, the clinical prevalence of ESR1 mutations in ER+ MBC may be much higher than previously reported. Both mutations appear to be associated with a more aggressive disease biology. Interestingly, these two activating mutations appear to have differential effects on EXE and EVE sensitivity, highlighting new areas for research in ER biology. Citation Format: Chandarlapaty S, Sung P, Chen D, He W, Samoila A, You D, Bhatt T, Patel P, Voi M, Gnant M, Hortobagyi G, Baselga J, Moynahan ME. cfDNA analysis from BOLERO-2 plasma samples identifies a high rate of ESR1 mutations: Exploratory analysis for prognostic and predictive correlation of mutations reveals different efficacy outcomes of endocrine therapy–based regimens. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr S2-07.

Background: BRCA1/2 mutation carriers (gBRCA) have a higher risk of breast or ovarian cancer, since BRCA1/2 mutation results in impaired high-fidelity DNA repair by homologous recombination (HR) and subsequently genetic instability. In non-gBRCA TNBC, HR deficiency occurs at the somatic level, by means of BRCA1 mutation, BRCA1 epigenetic loss or mutation in other HR-associated genes. Because PARP1/2 inhibitors (PARPi) are well-tolerated and active anti-cancer agents in the advanced setting of gBRCA tumors, we sought to expand their applicability by identifying response biomarkers in TNBC. Methods: We have assessed the antitumor response of the PARP1/2 inhibitor olaparib as single agent in a panel of 12 primary and advanced TNBC PDX models. On PDXs exhibiting primary sensitivity to olaparib, we have developed models of acquired resistance by continuous exposure to the drug and identifying progression on treatment. We have characterized the models through targeted sequencing and the analysis of the hypermethylation and expression levels of BRCA1 transcript to find potential correlates of drug-sensitivity. Results: Three out of 12 PDXs (25%) treated with single agent olaparib, exhibit tumor regression or disease stabilization. BRCA1 is hypermethylated in two of these PARPi-sensitive TNBC PDX models and is associated with loss of BRCA1 mRNA expression. The third PARPi-sensitive TNBC PDX harbors a frameshift, heterozygous PALB2 mutation, which is no longer detected in the acquired resistance PDX model. Acquired resistance in the hypermethylated PDXs is under study as well as the duration of response compared to gBRCA PDX models. Conclusions: Our study highlights that somatic HR-deficiency is frequent in TNBC and provides the basis of sensitivity to PARPi. Citation Format: Serra V, Cruz C, Bruna A, Ibrahim YH, Vivancos A, Vivancos A, Nuciforo P, Bellet M, Gómez P, Pérez JM, Saura C, Vidal M, Serres X, Rueda OM, Peg V, Caldas C, O'Connor MJ, Baselga J, Cortés J. PARP1/2 inhibition in a subset of triple negative breast cancer (TNBC) patient-derived tumor xenografts (PDX) identifies predictive biomarkers of response. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P4-07-04.

BACKGROUND: Pertuzumab (P) in combination with trastuzumab (T) and docetaxel (D) is the approved first line SOC in patients with HER2 positive metastatic breast cancer and is approved neoadjuvantly in patients with HER2 positive stage Ib-IIIc breast cancer. Because of its role in heterodimerization with EGFR, P may cause adverse events associated with EGFR antagonists. Diarrhea is the most commonly reported AE due to P. Increased usage of P has generated clinical questions regarding the incidence and management of diarrhea. Here we report safety analyses of diarrhea from three P containing studies. METHODS: The safety population evaluated in this exploratory analysis included 804 patients from CLEOPATRA, 416 patients from NeoSphere, and 223 from TRYPHAENA. Diarrhea incidence, severity (NCI-CTCAE v3.0), and management in P containing arms were analyzed. RESULTS: The incidence and management of diarrhea in MBC (Table 1), EBC (Table 2): CLEOPATRA P+T+D n=408Pla+T+D n=396Incidence of Events n (%)All Grades279 (68)193 (49)≥ Grade 338 (9)20 (5)Median time to 1st event (days) all grades / Interquartile Range (IQR)8 (4,44)23 (6,82)Discontinuation of any study drug8 (0.2)2 (0.6)Treatment n (%)Antidiarrheal treatment164 (40)77 (19) NeoSphere X4 followed by adjuvant FECx3TRYPHAENANeoadjuvant tx followed by T up to 1 yearT+D n=107P+T+D n=107P+T n=108P+D n=94FEC+P+T x3→P+T+D x3 n=72FEC x3 →P+T+D x3 n=75TCH+P x6 n=76Incidence of Events n (%) (neoadjuvant + adjuvant exposure)All Grades41 (38)55 (51)46 (43)53 (56)46 (64)47 (63)55 (72)≥ Grade 34 (4)7 (7)3 (3)5 (5)3 (4)4 (5)9 (12)Median time to 1st event (days) all grades / Interquartile Range (IQR)7 (4,24)8 (3,26)19 (4,117)6 (3,21)9 (4,30)69 (64,82)6 (3,21)Discontinuation of any study drug0000000Treatment n (%)Antidiarrheal treatment13 (12)23 (22)20 (19)28 (30)23 (32)22 (29)31 (41)pertuzumab(P)+trastuzumab(T)+docetaxel(D) FEC= 5FU, epirubicin, cyclophosphamide TCH= docetaxel,(T)carboplatin(C), trastuzumab(H) The overall incidence of diarrhea events is greatest in the first cycle containing P: in CLEOPATRA (P+T+D) 43%, in NeoSphere (P+T+D) 34%, (P+T) 21%, and in TRYPHAENA (FEC+P+T→P+T+D) 40%, (FEC→P+T+D c4) 46%, and (TCH+P) 55%. Of patients experiencing diarrhea, the median number of events (all grades) for patients receiving P+T+D in CLEOPATRA and NeoSphere was 2 and 1 respectively, and 2 for patients receiving TCH+P in TRYPHAENA. CONCLUSIONS: Diarrhea was common in all P containing arms but events were mostly low grade and occurred more often with the first cycle. Events and management were similar in the EBC and MBC setting. Approximately half of patients required antidiarrheal treatment. However, rates of study drug discontinuation due to diarrhea were low. Studies of treatment associated diarrhea management are planned. Citation Format: Swain SM, Schneeweiss A, Gianni L, Stein A, McNally V, Heeson S, Portera C, Yoo B, Cortes JC, Baselga J. Incidence and management of diarrhea in patients with HER2-positive breast cancer treated with pertuzumab. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P4-14-14.

Background: Taselisib is an orally bioavailable, potent, selective inhibitor of Class I PI3-kinase (PI3K) alpha, gamma, and delta isoforms, with 30-fold less inhibition of the PI3K beta isoform relative to the alpha isoform showing enhanced activity against PIK3CA mutant cancer cell lines. Clinical data have demonstrated confirmed partial responses in patients with PIK3CA mutant breast cancer (BC) treated with single-agent taselisib. Enhanced antitumor activity has been noted when taselisib is combined with either letrozole or fulvestrant in preclinical and Phase Ib clinical studies. Methods: LORELEI is a Phase II, two-arm, randomized, double-blind, multicenter, study of neoadjuvant letrozole and taselisib versus letrozole and placebo in postmenopausal women with newly diagnosed ER+/HER2-, untreated, Stage I-III operable BC. Other eligibility criteria include tumor size  2 cm by magnetic resonance imaging (MRI), ECOG PS 0-1, and evaluable tumor tissue for PIK3CA genotyping. Patients treated with anti-diabetic drugs are not eligible. Patients are randomized (1:1) to receive continuous letrozole (2.5 mg) with either taselisib (4 mg on a 5 days on/ 2 days off schedule) or placebo for 16 weeks, followed by surgery. Stratification is based on tumor size and nodal status. The co-primary endpoints are overall objective response rate (ORR) by centrally assessed breast MRI via modified RECIST criteria and pathologic complete response (pCR) rate in breast and axilla at time of surgery in all randomized patients and PIK3CA mutant patients. Secondary endpoints include ORR by centrally-assessed MRI and pCR rate in PIK3CA wild-type patients. The sample size was calculated to detect an absolute percentage increase of 24% in ORR with 80% power and an absolute percentage increase of 18% in pCR rate. An interim safety analysis will be conducted by an Independent Data Monitoring Committee. As of 1st Jun 2015, 54 of the 330 patients have been enrolled, and global enrollment is ongoing (clinicaltrials.gov NCT02273973). Contact information: Reference Study ID Numbers: GO28888/BIG-3-13/SOLTI 1205/ABCSG 38 Phone: 888-662-6728 (US Only) Email Address: global.rochegenentechtrials@roche.com Citation Format: Oliveira M, de Azambuja E, Saura C, Dubsky P, Zardavas D, Fesl C, Bardia A, Soberino J, Ciruelos Gil E, Ng V, Fredrickson J, Stout TJ, Singel SM, Hsu JY, Piccart M, Gnant M, Baselga J. LORELEI: A phase II randomized, double-blind study of neoadjuvant letrozole plus taselisib (GDC-0032) versus letrozole plus placebo in postmenopausal women with ER-positive/ HER2-negative, early-stage breast cancer. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr OT1-03-06.

Background: TNBC often exhibits activation of PI3K/Akt signaling, associated with loss of PTEN expression, low INPP4B expression, and/or increased AKT3 amplification. Inhibition of the PI3K/Akt pathway in diverse cancers leads to radiosensitization and/or chemosensitization. Ipat is an oral, potent ATP-competitive small molecule inhibitor of all three isoforms of Akt. The combination of ipat with taxanes in preclinical models resulted in enhanced efficacy relative to either ipat or chemotherapy alone. In a Phase Ib clinical study, the combination of ipat with diverse chemotherapy regimens was well-tolerated and resulted in RECIST responses, particularly pts with tumors having PI3K/Akt activation. Methods: FAIRLANE is a randomized, double-blind, placebo controlled, multicenter, neoadjuvant Phase II study designed to estimate the efficacy of ipat combined with pac versus placebo combined with pac in women with Stage Ia  IIIa TNBC. Approximately 150 pts (Pts) will be enrolled, randomized in a 1:1 ratio, and stratified by PTEN status, node involvement, and tumor size. Pts will receive 3 cycles of ipat 400 mg or placebo orally once daily on Days 1 to 21 of each 28-day cycle, along with pac 80 mg/m2 every 7 days for a total of 12 doses. All pts will undergo pretreatment and Day 8 tumor tissue acquisition to evaluate pathway biomarkers. Following three cycles of treatment, pts will undergo surgery. The primary efficacy endpoint, pCR within the breast and axilla (ypT0/Tis ypN0) in all pts and in pts with PTEN low tumors, will be assessed by local pathology evaluation following completion of neoadjuvant therapy and surgery. Additional endpoints include objective response rate, safety, BCS rate, pharmacokinetics, and pathway biomarkers. Following surgical resection of primary tumor, pts are expected to continue post-operative treatment with a standard adjuvant chemotherapy regimen at physician's discretion. The study is open for accrual. Clinical trial information: NCT02301988. Citation Format: Saura C, Isakoff SJ, Calvo I, Patt D, Andersen J, Gonzalez-Martin A, Fisher J, Ciruelos E, Gil-Gil M, De la Peña L, Choi Y, Jia S, Singel S, Patel PH, Baselga J, Oliveira M. FAIRLANE: A phase II randomized, double-blind, study of the Akt inhibitor ipatasertib (Ipat, GDC-0068) in combination with paclitaxel (Pac) as neoadjuvant treatment for early stage triple-negative breast cancer (TNBC). [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr OT1-03-09.

Background: PIK3CA mutations are one of the most frequent genomic alterations in breast cancer (BC), being present in ∼40% of estrogen receptor (ER)-positive, HER2-negative breast tumors. PIK3CA mutations promote growth and proliferation of tumors and mediate resistance to endocrine therapies in BC. Taselisib is a potent and selective PI3-kinase (PI3K) inhibitor that displays greater selectivity for mutant PI3Kα than wild-type PI3Kα. Taselisib has enhanced activity against PIK3CA-mutant BC cell lines, and clinical data include confirmed partial responses in patients with PIK3CA-mutant BC treated with taselisib either as a single agent or in combination with fulvestrant. Trial design: SANDPIPER is a double-blind, placebo-controlled, randomized, phase III study, designed to evaluate efficacy and safety of taselisib plus fulvestrant in patients with ER-positive, HER2-negative locally advanced or metastatic BC. Patients will be randomized 2:1 to receive either taselisib (4 mg daily) or placebo in combination with fulvestrant (500 mg intramuscular on Days 1 and 15 of Cycle 1, and on Day 1 of each subsequent 28-day cycle). Randomization will be stratified by visceral disease, endocrine sensitivity, and geographical region. The study enriches for patients with PIK3CA-mutant tumors who will be randomized separately from patients with non-mutant tumors. Eligibility: Postmenopausal women with ER-positive, HER2-negative, locally advanced or metastatic BC are eligible if they have disease recurrence or progression during or after aromatase inhibitor treatment. A valid PIK3CA-mutation result via central assessment is required prior to enrollment. Aims: The primary efficacy endpoint is investigator-assessed progression-free survival (PFS) in patients with PIK3CA-mutant tumors. Other endpoints include overall survival (OS), objective response rate (ORR), clinical benefit rate (CBR), duration of objective response, safety, pharmacokinetics, and patient-reported outcomes. Efficacy in patients without PIK3CA-mutant tumors will be an exploratory endpoint. Statistical methods: The primary efficacy analysis population will include all randomized patients with PIK3CA-mutant tumors. Patients will be grouped according to treatment arm assigned at randomization. Median PFS and OS will be estimated using Kaplan-Meier methodology in each treatment arm. Cox proportional-hazards models will be used to estimate the hazard ratio with 95% confidence intervals (CIs). ORR, CBR, and their 95% CIs will be estimated by treatment arms. Duration of objective response will be estimated by treatment arms using the Kaplan-Meier methodology. Quality of life will be analyzed and summarized by treatment arms. Safety will be analyzed for all treated patients according to actual treatment received. Accrual: Target enrollment is 600 pts from ∼165 sites and ∼23 countries. The study is open for enrollment and 11 patients have been enrolled as of May 31, 2015. Clinicaltrials.gov ID: NCT02340221. Contact information: For more information or to refer a patient, email global.rochegenentechtrials@roche.com or call 1-888-662-6728 (USA only). Citation Format: Baselga J, Cortés J, De Laurentiis M, Diéras V, Harbeck N, Hsu J, Jin H, Schimmoller F, Wilson TR, Im Y-H, Jacot W, Krop IE, Verma S. SANDPIPER: Phase III study of the PI3-kinase inhibitor taselisib (GDC-0032) plus fulvestrant in patients with estrogen receptor-positive, HER2-negative locally advanced or metastatic breast cancer enriched for patients with PIK3CA-mutant tumors. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr OT1-03-14.

ESR1 hotspot mutations have been identified in 30-40% of patients with ER+ MBC and promote resistance to aromatase inhibitors (AIs). Identification of these mutations has been aided by the use of plasma DNA for their detection, however many such tests only survey for hotspot mutations. In this study, we examined the prevalence, biologic and clinical significance of mutations in ESR1 that lie outside previously described hotspots (E380Q, Y537, D538G). Using next generation sequencing of tumor DNA from over 4000 patients with breast cancer, we have identified numerous somatic alterations in ESR1. Among the somatic alterations were mutations detected in the transcription activation function-1 (AF-1), DNA binding domain, dimerization interface and C-terminus of ER. We characterized the functional significance of these non-canonical mutations alongside hotspot mutations, starting with assays of ER driven transcription and deduced several classes of mutations: (1) mutations that weakly promote ligand-independent activity, (2) mutations that led to ligand-independent activity comparable to estradiol stimulation, and (3) mutations that resulted in impaired transcriptional activity. Class 2 mutations remain localized at amino acids 536-538, while the class 1 mutations are observed in various domains of ESR1, including the DNA binding domain and dimerization interface. Several Class 3 mutations were found in proximal to Helix 12, highlighting the critical role of this region. Clinically, non-canonical mutations were not exclusively observed among patients treated with AI, as there were several mutations from SERM/SERD treated patients. We thus examined the effects of different mutants on their sensitivity to ER antagonists, such as fulvestrant or tamoxifen. The data revealed key differences between the different classes of mutants; with majority of the class 2 mutants exhibiting reduced sensitivity to the antagonists compared to wild type. This also correlated with the relative binding affinities (RBA) of the mutants to fulvestrant and 4-hydroxytamoxifen, in which the RBA of class 2 mutants (Y537S and D538G) were significantly lower than wild type, perhaps accounting for their reduced sensitivities. Nevertheless, it appeared that all mutants could be effectively inhibited either by higher concentrations or more potent ER antagonists, implying a continued ability to distort ER into the antagonist conformation. Interestingly, several Class 1 mutants showed weak agonism in response to specific antagonists raising the possibility of their role in SERM/SERD resistance. Taken together, the data demonstrated that not all ESR1 mutations affect receptor function or respond to antiestrogen therapies similarly. These data also imply the importance of more broad sequencing coverage of ESR1 in the clinic to effectively capture the spectrum of biologically relevant alleles. Citation Format: Toy W, Carlson KE, Martin TA, Razavi P, Berger M, Baselga J, Greene G, Katzenellenbogen J, Chandarlapaty S. Non-canonical, clinical ESR1 mutations promote resistance to antiestrogen therapies [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P5-04-11.

This abstract was withdrawn by the authors. Citation Format: Di Cosimo S, Appierto V, Pizzamiglio S, Baselga J, Piccart M, Huober J, Izquierdo M, de la Pena L, Hilbers F, de Azambuja E, Untch M, Pusztai L, Pritchard KI, Nuciforo P, Salomon AV, Symmans FW, Apolone G, de Braud F, Verderio P, Daidone MG. Withdrawn [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P4-01-03.

Background: MBC is a clinically heterogeneous disease that cannot be cured with currently available treatment options. Selective approaches are needed to identify patient subgroups with different tumor sensitivities who will benefit the most from available therapies for MBC. PM01183 (P), also known as lurbinectedin, is a new anticancer drug that binds to the DNA minor groove inducing both double-strand breaks and transcription blocking. It has significant in vitro and in vivo activity against several tumor models, particularly breast cancer. P is more active against homologous recombination (HR)-deficient cell lines; hence, MBC patients (pts) with deleterious germline BRCA mutations might be more sensitive to P than sporadic tumors. Methods: A multicenter, open-label, phase II study of P (7.0 mg fixed dose) as 1-hour intravenous infusion every 3 weeks in pts with MBC with or without known BRCA1/2 mutation at study entry. To be enrolled, pts must be women 18-75 years old with confirmed MBC pretreated with 1-3 chemotherapy regimens for MBC (including at least one prior trastuzumab-containing regimen for HER-2 overexpressing pts), measurable disease as per RECIST v1.1, performance status (PS) of 0-1 and adequate major organ function. Pts are excluded if pretreated with P, trabectedin, or radiotherapy (RT) on >35% of bone marrow; if they have prior/concurrent malignant disease not in complete remission for >5 years, clinically unstable central nervous system involvement, and other diseases/situations that might increase patient's risk; if they are pregnant or lactating women; or if they require RT. Aims: The primary aim is to determine the antitumor activity of P, in terms of overall response rate (ORR), in two cohorts of MBC pts: BRCA+ (with known BRCA1/2 mutation), and unselected (with BRCA1/2 wild type or unknown mutation status). Secondary aims are to determine duration of response, clinical benefit (response or stable disease > 3 months), PFS and one-year overall survival; to evaluate whether presence of BRCA1/2 mutation predicts response to P in MBC; to explore the activity of P in specific MBC subpopulations, safety, pharmacokinetics (PK), PK/pharmacodynamic correlations, and pharmacogenomics. Planned enrollment is 117 evaluable pts: 53 in the BRCA+ cohort and 64 in the unselected cohort. P will be considered effective if confirmed objective response is achieved in ≥ 17 BRCA+ pts and ≥ 12 unselected patients. An ORR-based futility analysis will be conducted when 20 and 30 evaluable pts have been recruited in each cohort, respectively. If Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr OT1-4-01.

Background: HER2-amplified (HER2+) breast cancer is biologically heterogeneous and all the intrinsic molecular subtypes (Luminal A, Luminal B, HER2-enriched and Basal-like) can be identified. However, the molecular and outcome differences of the intrinsic subtypes based on HER2 status have not been thoroughly studied. This is important since HER2 is considered an oncogene involved in the activation of various signal transduction pathways, as well as a biomarker of poor prognosis (in the absence of anti-HER2 targeting). Methods: To compare molecular features between clinically HER2+ and HER2-negative tumors, we interrogated The Cancer Genome Atlas (TCGA) publicly available dataset of 825 primary breast cancers with at least one of following data types: mRNA expression (17,784 genes), protein expression (171 proteins and phospho-proteins), DNA methylation status (574 probes), miRNA expression (306 transcripts) and whole exome somatic mutations. Two-class unpaired Significant Analyses of Microarrays were used to identify significant biomarker associations with a False Discovery Rate of 0%. For survival associations, we interrogated the METABRIC DNA copy number/gene expression-based dataset (Curtis et al. Nature) composed of 1,971 primary breast tumors with long-term clinical follow-up (and no adjuvant anti-HER2 therapy). Multivariable Cox models were used to test the prognostic significance of each variable. The research based 50-gene PAM50 model was used to classify tumors into the different intrinsic subtypes. Results: In both datasets combined (n = 2,225), HER2+ disease showed an enrichment for HER2-enriched tumors (47.0% vs. 7.1%) and a decrease in Luminal A tumors (7.3% vs. 39.0%) compared to HER2-negative disease (p Conclusions: When the intrinsic subtypes are taken into account, HER2 amplification does not translate into large changes in the activation of downstream signaling pathways or worse patient survival outcomes. These results also suggest that the potential responses to anti-HER2 therapy on HER2-amplified tumor cells depend in part upon their intrinsic tumor profile. Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P4-12-01.

Background: Preclinical studies indicate that the dual inhibition of IGFR and mTOR may be additive or synergistic and abrogates the feedback activation of AKT due to rapamycin analog mTOR inhibitors. A phase 1 study of the mTOR inhibitor RIDA and the anti-IGFR antibody DALO demonstrated that the combination was feasible and well-tolerated at doses that were nearly those used for the two single agents. The dose limiting toxicity was stomatitis, similar to RIDA monotherapy. Preliminary signals of anti-tumor activity, including partial responses and prolonged progression free survival (PFS), were observed in ER+ advanced breast cancer (ABC), especially in high proliferation tumors (Ki67 ≥15%). Methods: The trial was a multi-center, international randomized study with PFS as the primary endpoint. Key eligibility included ABC with prior treatment with a non-steroidal aromatase inhibitor. The original phase 2 study design was a two-part, adaptive design intended to first test the combination of RIDA (30 mg by mouth daily for 5 out of every 7 days), -DALO (10 mg/kg IV weekly) against a standard agent, exemestane in Part A. Patients were stratified into high and low proliferation strata based on baseline Ki67. Following a demonstration of PFS benefit of the combination in Part A, Part B was intended to show the PFS benefit of the combination over each single agents by comparing RIDA-DALO to RIDA and DALO. Results: The study was initiated in October 2011. Accrual was suspended after the first 66 patients were randomized due to a higher than expected rate of stomatitis in the RIDA-DALO arm. Preliminary data indicated an overall incidence of any grade stomatitis was 68% (22/33 pts), and of grade 3 stomatitis was 35% (11/33 pts). In an effort to identify a more tolerable regimen, the study was amended to eliminate Part B and to evaluate two sequential reduced dose RIDA-DALO cohorts in a non-randomized design: 20mg and 10mg for 5 out of every 7 days. The dose of DALO was unchanged. Preliminary safety results of overall and grade 3 stomatitis in the 20 mg were 81.5% (22/27 pts) and 37% (10/27 pts), respectively. Although the incidence of overall stomatitis in the 10 mg cohort remained high, 88% (22/25 pts), grade 3 stomatitis was dramatically reduced to 8% (2/25 pts). Conclusion: Preliminary evaluation of safety from this phase 2 study demonstrates that the previously recommended phase 2 dose of RIDA-DALO was not tolerable. However lower doses of RIDA (10 mg) in combination with DALO appeared to be tolerable with markedly reduced rates of grade 3 stomatitis. Final results of efficacy, safety and RNA profiling analysis from the two RIDA-DALO dose cohorts as well as from the randomized portion of the study will be available at the time of the meeting. Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P2-16-04.

Background: CLEOPATRA is a phase III study of placebo (Pla)+T+D and P+T+D in HER2-positive first-line MBC. The combination of both HER2-targeted antibodies, P+T, with D resulted in significantly improved progression-free survival (PFS) and overall survival (OS). The incidence of febrile neutropenia (FN) was higher with P+T+D versus Pla+T+D. We present analyses of adverse events (AEs) and treatment patterns for pts from Asia. Methods: Pts were from Asia, Europe, North and South America. Study drugs were given intravenously, q3w: P/Pla, 840 mg initial dose, then 420 mg; T, 8 mg/kg initial dose, then 6 mg/kg; D, 75 mg/m2 with escalation to 100 mg/m2 if tolerated. Treatment was given until disease progression or unacceptable toxicity; 6 cycles of D were recommended, >6 cycles were at investigator's discretion. Dose modifications of P or T were not permitted. Two D dose reductions by 25% to 75 mg/m2 and 55 mg/m2 were allowed in order to manage toxicities; re-escalation was not permitted. Results: The safety population comprised 253 pts from Asia (Pla+T+D: 128; P+T+D: 125) and 551 pts from other regions (Pla+T+D: 269; P+T+D: 282). The incidences of neutropenia, FN, diarrhea, mucosal inflammation, grade ≥3 AEs overall, and serious AEs were higher with P+T+D versus Pla+T+D. In the P arm, the largest increase in AEs in pts from Asia versus other regions was observed for FN and mucosal inflammation. D dose was more frequently reduced in pts from Asia; however, the incidence of AEs leading to discontinuation of all study treatment was balanced between pts from Asia and other regions. PFS and OS were improved with P+T+D in pts from all regions. In the whole study population, the hazard ratios (HR) for PFS and OS were 0.63 (95% CI 0.52-0.76) and 0.66 (0.52-0.84), respectively. In pts from Asia, the HR was 0.68 (0.48-0.95) for PFS and 0.64 (0.41-1.00) for OS. These efficacy analyses were unstratified. Pts with event, n (%)Other regionsAsia Pla+T+DP+T+DPla+T+DP+T+D n = 269n = 282n = 128n = 125Neutropenia123 (46)141 (50)74 (58)74 (59)FN15 (6)24 (9)15 (12)32 (26)Diarrhea118 (44)179 (63)66 (52)93 (74)Mucosal inflammation56 (21)67 (24)23 (18)46 (37)Grade ≥3 AEs194 (72)199 (71)95 (74)103 (82)Serious AEs69 (26)82 (29)35 (27)58 (46)AEs leading to discontinuation of all study treatment15 (6)21 (7)6 (5)4 (3)D dose escalation to 100 mg/m256 (21)47 (17)5 (4)1 (1)D dose reduction to Conclusions: AEs did not result in reduction of the median number of cycles administered in pts from Asia compared with other regions. However, given that 47% of pts from Asia had D dose reductions Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P4-12-10.

Introduction Assessment of PTEN might be an important tool in identifying patients unlikely to derive substantial benefit from trastuzumab and lapatinib-based therapies. Current studies failed to demonstrate an unequivocal predictive role of PTEN in human epidermal growth factor receptor-2 (HER2)-positive breast cancer both in neo-adjuvant and adjuvant settings. Lack of standardization of PTEN status determination in formalin fixed paraffin embedded (FFPE) tissue samples together with the small datasets analyzed in previous studies may have contributed to conflicting PTEN results and high variability of PTEN loss rates reported (22%-64%). Methods In the present study we have conducted a preliminary analysis investigating the influence of the antibodies, scoring methods and cutoff criteria used, together with the impact of inter-observer variability on PTEN status determination. Core biopsies from 429 FFPE baseline samples from early-stage HER2-positive breast cancer patients prospectively collected in the neoALTTO trial were stained with two widely used anti-PTEN monoclonal antibodies (clone 6H2.1 from DAKO and clone 138G6 from Cell Signaling Technology-CST). Two different pathologists independently scored the slides using the H-score system. Two different cut-off criteria were used to define PTEN loss of expression: H-score < 50 and ≤10% positive staining (any level of intensity). Results Out of 429 processed samples, 363 and 369 were evaluable for observer 1 (CST and DAKO, respectively) and 367 were evaluable for observer 2, with an average missing rate of 15%. A strong linear correlation was observed between CST and DAKO antibodies for both observers (R2 > 0.7). After setting a cutoff for PTEN loss, the observed discordance rate was below 10%, with the number of discordant cases ranging from 28 to 33 (depending on the cut-off criteria and observer). Inter-observer correlation was strong with both antibodies (R2 = 0.8). Based on the cutoff criteria and antibodies used, inter-observer discordance rates ranged between 6% and 10%; the lowest rate observed at ≤10% cutoff threshold with CST antibody. PTEN was classified as “loss” in 23%, 19%, 16%, and 13% of cases by observer 1 and in 32%, 29%, 24%, 19% of cases by observer 2 using DAKO H-score Conclusion Our preliminary analysis showed high inter-antibody and inter-observer concordant rates for PTEN status determination by IHC. However, the lack of a standardized definition of PTEN cutoff thresholds for defining negativity and positivity generated loss call rates ranging from 13% to 32% within the same dataset. Correlative analyses with pCR and PIK3CA status are ongoing to determine the impact of PTEN expression and its variability in predicting response to single-agent or dual HER2 targeting. Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr PD1-7.

Background: The clinical benefit of combination of mTOR inhibition and anti-hormonal therapy has been previously established and represents a new standard of care for patients with hormone receptor positive (HR+) advanced breast cancer (ABC). Preclinical evaluation of the mTOR pathway demonstrates that dual inhibition of IGFR and mTOR may be additive or synergistic and abrogates the feedback activation of AKT due to rapamycin analog mTOR inhibitors. A completed phase 1 study of the combination of the mTOR inhibitor, RIDA and the anti-IGFR antibody, DALO demonstrated preliminary signals of anti-tumor activity. This was further evaluated in a recently completed phase 2 study of RIDA-DALO compared to exemestane in ER+ ABC. Final safety and efficacy results from that phase 2 study will be reported at this meeting (see Baselga et al). Building upon the clinical synergies of mTOR and EX as well as the biologic relationship of the mTOR and IGFR pathways, a clinical study has been initiated to evaluate the triplet combination of RIDA-DALO-EX compared to RIDA-EX. Methods: This is a multicenter, international, randomized phase 2 study of the triplet combination of RIDA (10 mg by mouth daily for 5 out of every 7 days), DALO (10 mg/kg IV weekly), and EX (25 mg QD) compared to RIDA (30 mg by mouth daily for 5 out of every 7 days) and EX (25 mg QD) in high KI67 (≥15%) expressing ER+, ABC. Approximately 84 patients will be randomized 1:1 to either triplet or doublet therapy. Key eligibility criteria include: HR+ and HER-2 negative measurable ABC, prior therapy with a non-steroidal aromatase inhibitor, and KI67 labeling index ≥15%. The primary endpoint of the study is progression free survival (PFS). Key secondary endpoints include evaluation of percent (%) reduction from baseline in the sum of imaging measurements (target lesion diameters or volumes) at 16 weeks between the two arms, and overall response rates. The sample size is event driven with a target of 38 PFS events, which provides approximately 80% power, at 1-sided alpha of 0.1, to detect a HR of 0.5, corresponding to an approximate 100% improvement in median PFS, from 10.6 to 21.2 months. Safety parameters or adverse experiences of special interest include hyperglycemia, stomatitis, mucosal inflammation, pneumonitis and hearing loss. Accrual has been completed with results expected in May 2014. Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr OT2-6-13.

Background: Pathological complete response (pCR) is a proposed surrogate endpoint for predicting long-term clinical benefit on endpoints such as event-free survival (EFS) or overall survival (OS). The CTNeoBC meta-analysis did not validate the surrogacy of pCR for EFS or OS, and there is no precedent for its use as a regulatory endpoint in oncology. Use of the accelerated approval pathway has been proposed for neoadjuvant therapies that substantially improve pCR as a means to expedite widespread access to highly effective therapies for high-risk, early breast cancer. Potential risks of this approach include approving an agent that ultimately does not demonstrate clinical benefit and, in the interim, exposing curable patients to the toxicity of therapy without certainty of benefit. To mitigate the risks of this pathway, enrollment to neoadjuvant trials intended to support accelerated approval should be restricted to patients presenting with high-risk early-stage breast cancer. The 5-year EFS rate by breast cancer subtype in the CTNeoBC meta-analysis population is presented. Methods: We identified 12 neoadjuvant randomized trials (N = 12,993) with pCR clearly defined and long-term follow-up available for EFS and OS. Trials included AGO 1 (n = 668), ECTO (n = 1355), EORTC 10994/BIG 1-00 (n = 1856), GeparDuo (n = 907), GeparQuattro (n = 1495), GeparTrio (n = 2072), GeparTrio-Pilot (n = 285), NOAH (n = 234), NSABP B18 (n = 760), NSABP B27 (n = 2411), PREPARE (n = 733), and TECHNO (n = 217). The key objective of this analysis was to establish a definition of “high-risk” based on the Kaplan-Meier estimates of the 5-year EFS rate in the different clinical breast cancer subtypes (hormone receptor-positive, HER2-positive and triple-negative) analyzed by tumor stage and tumor grade at presentation. Results: The 5-year EFS rate was less than 65% in all the breast cancer subtypes with stage III disease. For patients with stage II disease, the impact of tumor grade varied by hormone receptor status. Patients with hormone receptor-negative breast cancer, regardless of HER2 status had a poor prognosis that was independent of tumor grade. For patients with hormone receptor-positive tumors, regardless of HER2 status, high grade histology was associated with an increased risk of recurrence. 5-year Event-Free Survival Rate (EFS) 5-year EFS Rate Estimate (95% confidence interval)TNMStage IIStage III Grade IIGrade IIIGrade IIGrade IIIHormone Receptor + HER2-83% (80%, 85%)71% (65%, 77%)63% (58%, 69%)51% (42%, 59%)HER2+ HR+81% (75%, 86%)69% (60%, 76%)50% (41%, 59%)48% (37%, 59%)HER2+ HR-61% (51%, 70%)66% (57%, 73%)58% (46%, 69%)46% (36%, 55%)Triple Negative66% (58%, 72%)72% (67%, 76%)38% (27%, 48%)37% (29%, 45%) Conclusions: This analysis estimated the 5-year EFS rate in the breast cancer subtypes from the CTNeoBC meta-analysis population. The HER2-positive population in the meta-analysis was at particularly high risk because most of the patients had locally advanced breast cancer and only 39% of these patients received trastuzumab therapy. We propose defining less than 75% 5-year EFS rate as “high-risk” for the purposes of designing neoadjuvant trials that intend to use pCR to support accelerated approval. Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P5-17-01.

Background: The PI3K/Akt/mTOR pathway is frequently activated in breast cancer (BC) and is important for the oncogenic function of HER2. Buparlisib is an oral pan-PI3K inhibitor that targets all 4 isoforms of class I PI3K (α, β, γ, Δ). Preliminary clinical activity was observed with buparlisib in patients (pts) with advanced BC as a single agent, and in combination with paclitaxel (Dirix et al. ESMO 2012) or trastuzumab (Pistilli et al. ESMO 2012). Study design: NeoPHOEBE (NCT01816594) is a Phase II, randomized, double-blind, parallel-cohort study of neoadjuvant buparlisib or matched placebo plus trastuzumab and weekly paclitaxel. Upfront stratification of pts into 2 independent cohorts according to PIK3CA mutation status will determine whether pts with PIK3CA-mutant tumors may benefit more from this treatment combination. Adult women with newly diagnosed, HER2-positive, primary non-inflammatory BC who have not previously received systemic therapy for invasive disease are eligible. Other eligibility criteria: tumor size >2 cm; unilateral disease; available tumor tissue for central review of estrogen receptor (ER) and HER2 status, and PIK3CA genotype; known PIK3CA mutation status; and ECOG PS ≤1. Pts in each cohort (PIK3CA mutant or wild-type [wt]) are randomized (1:1) to receive continuous daily buparlisib (100 mg) or placebo and weekly trastuzumab (4 mg/kg loading dose then 2 mg/kg) for 6 weeks, followed by continuous daily buparlisib (80 mg) or placebo with weekly trastuzumab (2 mg/kg) and weekly paclitaxel (80 mg/m2) for 12 weeks. Study treatment is followed by surgery within 4 weeks of last paclitaxel dose. Stratification at randomization is based on PIK3CA (mutant vs wt) and ER (positive vs negative) status. Endpoints: All endpoints will be measured in both PIK3CA-mutant and wt cohorts. The primary endpoint is rate of pathologic complete response (pCR; ypT0) at time of surgery. The key secondary endpoint is objective response rate (ORR) at the end of week 6. Other secondary endpoints include pCR by other definitions, ORR prior to surgery, pCR and objective response by ER status, percent of pts with node-negative disease at surgery, rate of breast conserving surgery, and safety. Exploratory objectives include change in standardized uptake value (SUV) at Day 15 by FDG-PET; and ORR and pCR by PTEN expression, Ki67 level, apoptosis rates, percentage of tumor infiltrating lymphocytes (TIL), and by phenotype of 50% TIL at baseline. Statistical methods: The sample size is based on a minimax 2-stage randomized Phase II design with a prospective control. This design allows for early stopping if the desired efficacy is not observed after stage 1. Both cohorts are powered (80%) to detect a clinically meaningful increase in pCR of 18% at a one-sided significance level (α = 0.15). Target accrual: Planned enrollment for NeoPHOEBE is up to 220 pts at 65 sites in 12 countries across South America, Europe, and Asia-Pacific. Contact: For further study information, contact BIG@bordet.be. Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr OT2-6-08.

The mammalian target of rapamycin (mTOR) protein kinase regulates protein translation and proliferation by integrating the availability of energy, nutrients and the presence of growth factors. Dysregulation of mTOR is a common event in human tumors and results from mutational activation of receptor tyrosine kinases, PI3K signaling or inactivating mutations of the Tuberous Sclerosis or GATOR complexes as well as the LKB/AMP kinase pathway. The prevalence of mTOR activation in cancer has led to the development of two classes of inhibitors of the protein as therapeutics: the natural product rapamycin and its analogs as well as direct inhibitors of mTOR kinase. mTOR exists in at least two multi-protein complexes. The mTORC1 complex phosphorylates S6K and 4EBP and stimulates protein translation, metabolism as well as other processes. The mTORC2 complex phosphorylates and activates AKT and other AGC kinases. Rapamycin binds to the immunophilin FKBP12. Drug-bound FKBP12 complex binds to mTOR FRB domain and selectively inhibits the activity of mTORC1. However, rapalogs preferentially inhibit S6K phosphorylation compared to 4EBP phosphorylation. Rapalogs have undergone extensive clinical testing and have significant antitumor activity in renal cell and pancreatic neuroendocrine tumors and, in combination with aromatase inhibitors, in resistant, ER positive breast cancers. In contrast, mTOR kinase inhibitors suppress both mTORC1 and mTORC2 functions and potently inhibit S6K, 4EBP and AKT S473 phosphorylation. These drugs are in early clinical testing. In order to better understand the mechanism of action of these drugs and potential mechanisms of tumor escape from mTOR inhibition, we selected breast tumor cells for resistance to growth inhibition in cell culture by treatment with either rapamycin or an mTOR kinase inhibitor. In rapamycin resistant cells, phosphorylation of S6K and S6 were insensitive to the drug, but remained sensitive to mTOR kinase inhibitors. Conversely, in clones resistant to mTOR kinase inhibitors, mTORC1 and mTORC2 substrates were insensitive to the drugs, but S6K and S6 phosphorylation remained sensitive to rapamycin. Deep sequencing results explained these findings: rapamycin resistant clones harbored mutations in the FRB domain of mTOR, in the sites shown to interact with the FKBP12-rapamycin complex; mTOR kinase resistant clones harbored mutations in the mTOR catalytic domain. These mutations were not observed in the parental cells. It is likely that the mutations identified in each domain prevent binding of the drug. Consistent with these data, growth of rapamycin resistant cells retain sensitivity to mTOR kinase inhibitors and mTOR kinase resistant cells retain sensitivity to rapalogs, both in tissue culture and in vivo. The results suggest that tumor cells with acquired resistance to mTOR inhibitors retain a requirement for mTOR signaling for proliferation. Furthermore, tumors resistant to either class of drug may not be cross-resistant to the other and combined therapy with both might delay the onset of resistance. Further studies on the genetics of human tumors with acquired resistance to these agents will determine the clinical importance of these findings. Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr PD1-8.