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Background: The HER2 antibody drug conjugate (ADC) fam-trastuzumab deruxtecan-nxki (T-DXd) significantly improves outcomes over standard chemotherapy in pts with HER2-LOW (IHC 1+ and IHC 2+ FISH-) metastatic breast cancer (MBC). Data from the DAISY (NCT04132960) trial in pts with HER2 IHC 0 or “ultra low” MBC revealed median progression-free survival (PFS) of 4.2 mos vs 6.7 mos in HER2-LOW and 11.1 mos in HER2 3+ pts (Diéras V, et al. Cancer Res. 2022;82(4_Suppl):PD8-02). There is an urgent need to develop methods to accurately discern HER2 LOW expression versus HER2 IHC 0/ultra-low expression so appropriate pts may receive T-DXd. We have developed a quantitative HER2 assay using reverse phase protein array (RPPA) technology with laser capture microdissection (LCM) enrichment of tumor epithelium that measures HER2 expression over a 65-fold dynamic range in HER2 IHC 0 to 3+ breast cancers. In I-SPY 1 and 2 trials we found that RPPA-assessed quantitative HER2 and activated/phosphorylated HER2 expression predicted for pathologic complete response in pts with HER2 IHC 0, HER2-LOW and HER2 3+ disease with various HER2 and other targeted agents. We then developed and validated the first CLIA/CAP-accredited quantitative HER2 protein expression and activation assay, and now explore quantitative HER2 expression in HER2 IHC 0/ultra low disease. Given the recent approval of sacituzumab govitecan-hziy in TNBC and the results of the TROPiCS-02 (NCT03901339), we also evaluated quantitative RPPA-based TROP-2 expression levels in HER2 IHC 0 breast cancer. Methods: LCM-enriched tumor epithelium was obtained from freshly cut FFPE core needle and resected breast cancer samples from 175 pts with pathology-determined HER2 IHC 0 status (N=68 ER+ and N=107 ER-). Quantitative HER2 output is generated as a relative intensity unit (RU) that is interpolated to an internal calibrator curve and a population referent comprised of known HER2+ (IHC 3+ and 2+/FISH+), HER2-LOW and HER2 IHC 0/ultra-low tumors to generate population-based cut-points as a referent. RPPA-based quantitative HER2 expression are reported as one of four levels of expression across the HER2 dynamic range observed: “non/extremely low”, “modest“, “moderate”, and “high”. Quantitative TROP2 protein expression levels were also measured for each case by the RPPA assay on the same lysate using the same adjectival determinants of relative expression as HER2. Results: For the HER2 IHC 0 ER+ cohort, we observed HER2 protein expression over a 25-fold dynamic range and that 57% (N=39) had HER2 non/extremely low, 37% (N=25) modest, and 4 (6%) moderate/high HER2 expression by RPPA. For the HER2 IHC 0 ER- cohort, we observed HER2 protein expression over a 15-fold dynamic range and that 71% (N=76) had non/extremely low, and 31% (N=29%) modest HER2 expression. We observed TROP-2 protein expression over a 35-fold dynamic range across all tumors measured, and it was found to be at least modestly expressed in 95% (37/39) ER+ and 95% (72/76) ER- of the IHC 0/ultra-low tumors that were also found to be HER2 non/extremely low by RPPA. Conclusions: LCM-RPPA quantitative assessment of HER2 expression showed that nearly 40% of ER+ IHC 0 and 30% of ER- IHC 0 “ultra-low” breast cancers actually had modest to moderate HER2 expression. Interestingly, this frequency approximates the response rate of 30% seen with T-DXd in HER2 IHC 0 pts in the DAISY trial. Quantitatively measured TROP2 is at least modestly expressed in the vast majority of RPPA-assessed HER2 IHC 0 cancers regardless of ER status, making a TROP2-directed ADC an attractive therapeutic option for these pts. If validated in larger studies, LCM-RPPA-based HER2 expression could provide a better understanding of the potential for therapeutic efficacy with T-DXd in patients with HER2 IHC “ultra-low” disease, and may better define true ultra-low HER2 expression in HER2 IHC 0 tumor biopsies at baseline and refine the lower limit of the HER2-LOW designation. Citation Format: Emanuel F. Petricoin, Brian A. Corgiat, Joyce O’Shaughnessy, Patricia LoRusso, Kris Weinberg, Justin Davis, Chelsea Gawryletz. HER2-17 Novel Quantitative HER2 Assay for Determining Dynamic HER2 Expression in the HER2 IHC 0 “Ultra-Low” Setting: Implications for Precision Therapy in HER2- Breast Cancer [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr HER2-17.

Title: Drug target activation mapping of matched triple negative primary and axillary LN metastases identifies and links the ER-AR-GR steroid hormone receptor axis with downstream AKT activation Background: Triple negative breast cancer (TNBC) is comprised of heterogeneous subtypes that arise from various molecular alterations that result in TNBC having the poorest overall prognosis. There is growing interest in more sensitive ways to measure estrogen receptor (ER) and HER2 levels in the ER “negative” and HER2 “low/negative” settings, as there are patients with TNBC whose tumors are actually ER and/or HER2 “expressing/active”, and who may benefit from ER- and/or HER2-targeted therapies. Given the limitations of IHC in reliably quantitating ER and HER2 in low (0-1+) expressing tumors, we utilized highly sensitive reverse phase protein array (RPPA) to quantitate expression of these therapeutic targets along with downstream signaling activation mapping in a unique pilot set of patient-matched primary (P) and axillary lymph node (LN) metastases obtained synchronously. The quantitative expression of steroid hormone receptor expression/activation (ER, glucocorticoid receptor (GR), androgen receptor (AR)) along with their signaling architecture and dynamics were analyzed. Methods: A 12 P-LN paired tumor set was chosen for analysis (N=24). Manual macrodissection was used to enrich for tumor epithelium prior to RPPA analysis that quantitatively measured 155 proteins/phosphoprotein drug targets in key signaling pathways known to be involved in steroid hormone receptor biology and tumorigenesis. Statistical analysis using paired sample t-testing or Wilcoxon rank testing was performed (p< 0.05 uncorrected). Results: Protein pathway activation mapping and unsupervised clustering analysis revealed a subset of TNBCs from 3 of the 12 (25%) patients (N=4: 1 LN and 1 P, and one patient-matched LN and P) that was characterized by high relative levels of total ER. Interestingly, these same tumors also had amongst the highest relative levels of both total AR and activated (phosphorylated) GR compared to the rest of the 20 tumor samples. Downstream signaling analysis found significant (p< 0.05) activation/phosphorylation of AKT (S473 and/or T308) associated with the ER-AR-GR/steroid hormone activated/”high” TNBC signature compared to the 20 tumors that were steroid hormone “low”. Conclusions: Functional protein pathway activation mapping of a unique study set of synchronously obtained TNBC primary and LN metastasis revealed a steroid hormone receptor expression/activation signature of co-incidentally activated/expressed ER, GR and AR, that was also characterized by increased AKT activation (p< 0.05). This steroid hormone receptor “activated” signature was not observed to be significantly differentially expressed in LN compared to P tissues in cohort or matched pair analysis, suggesting that this signature may be present as an intrinsic event in the P, and not acquired in LN metastases. Recent data from stage I-III TNBC patients treated in the neoadjuvant setting with an AKT inhibitor1 revealed that responding TNBC patients had pre-treatment tumor biopsies that were enriched for both high AR expression and high phosphoAKT (S473 and/or T308) levels. If these observations that a subset of TNBCs are steroid hormone receptor “activated” despite being ER “negative” are confirmed in larger study sets, we hypothesize that this subgroup, identified by RPPA analysis of both P and LN metastases, could be potentially sensitive to AKT inhibition in combination with agents that target steroid hormone receptors. 1Shi Z, et al. Functional Mapping of AKT Signaling and Biomarkers of Response from the FAIRLANE Trial of Neoadjuvant Ipatasertib plus Paclitaxel for Triple-Negative Breast Cancer. Clin Cancer Res. 2022 Mar 1;28(5):993-1003 Citation Format: Julia Wulfkuhle, Page Blas, Heather Williams, Claudius Mueller, Rosa I. Gallagher, Mariaelena Pierobon, Joyce O’Shaughnessy, Emanuel F. Petricoin. PD5-08 Drug target activation mapping of matched triple negative primary and axillary lymph node metastases identifies and links the ER-AR-GR steroid hormone receptor axis with downstream AKT activation [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr PD5-08.

Background Adjuvant abemaciclib (a CDK4 and 6 inhibitor) combined with ET resulted in significant and clinically meaningful improvement in invasive disease-free survival (IDFS) and distant relapse-free survival (DRFS) in patients (pts) with HR+, HER2-, node-positive, high risk EBC in the monarchE trial, and is an approved adjuvant therapy for these patients. Here we present efficacy results from a pre-specified overall survival interim analysis (OS IA2) which was planned to occur 2 years (yrs) after the primary outcome analysis. Methods Pts were randomized (1:1) to receive ET for up to 10 yrs +/- abemaciclib for 2 yrs (study treatment period). High-risk EBC was defined as either ≥4 positive axillary lymph nodes (ALN), or 1-3 ALN with either Grade 3 disease and/or tumor ≥5 cm (Cohort 1). While the proliferation biomarker Ki-67 was centrally assessed in all pts with available tissue sample, an additional smaller group of pts with 1-3+ ALN and central Ki-67 ≥20% as the only high-risk feature were included (Cohort 2). The intent-to-treat (ITT) population consisted of both Cohort 1 (5120 pts) and Cohort 2 (517 pts). Hazard ratios (HR) were estimated using Cox proportional hazard model. Results At a median follow-up of 42 months, all pts were off abemaciclib. IDFS and DRFS data illustrate a sustained benefit beyond the treatment period. In the ITT population, the HR for IDFS was 0.664 (95% CI: 0.578, 0.762) and DRFS was 0.659 (95% CI: 0.567, 0.767). At 4 yrs, this reflected an improvement in IDFS rates from 79.4% to 85.8% (absolute difference 6.4%), and in DRFS rates from 82.5% to 88.4% (absolute difference 5.9%). The continued separation of the curves was associated with an increase in absolute benefit in IDFS 4-year rates compared to 2-and 3-year IDFS rates (absolute difference 2.8% and 4.8% respectively). While OS remained immature, there was a lower number of deaths observed in the abemaciclib plus ET arm compared to the ET alone arm (157 [5.6%] vs 173 [6.1%], HR 0.929 [95% CI: 0.748, 1.153], p = 0.503), suggesting that the robust benefit in IDFS and DRFS began to translate into a numerically favorable OS HR. As previously described, within Cohort 1, a Ki-67 index of ≥20% was associated with a worse prognosis, but similar abemaciclib treatment effects were observed regardless of Ki-67 index. No new safety signals were observed. Conclusion The clinically meaningful benefit of adjuvant abemaciclib added to ET in HR+, HER2-, node-positive, high-risk EBC persists beyond completion of abemaciclib therapy, yielding an increase in absolute IDFS and DRFS benefit at 4 yrs. While OS remains immature at this time, the lower number of deaths in the abemaciclib arm compared to the ET arm suggest that a survival signal favoring abemaciclib is emerging. Citation Format: Stephen Johnston, Masakazu Toi, Joyce O’Shaughnessy, Priya Rastogi, Mario Campone, Patrick Neven, Chiun Sheng Huang, Jens Huober, Georgina Garnica Jaliffe, Irfan Cicin, Sara Tolaney, Matthew P. Goetz, Hope Rugo, Elżbieta Senkus, Laura Testa, Lucia Del Mastro, Chikako Shimizu, Ran Wei, Ashwin Shahir, Maria Munoz, Belen San Antonio, Valerie Andre, Nadia Harbeck, Miguel Martín. Abemaciclib plus endocrine therapy for HR+, HER2-, node-positive, high-risk early breast cancer: results from a pre-planned monarchE overall survival interim analysis, including 4-year efficacy outcomes [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr GS1-09.

Background: The Theralink Reverse Phase Protein Array-based (RPPA) CLIA assay is a novel molecular assay developed to assist physicians in therapy selection for patients diagnosed with advanced/recurrent breast cancer. The assay was specifically designed to quantitatively measure protein activation/phosphorylation of 32 FDA-approved and Phase III drug targets and pathway-linked downstream substrates, providing functional information on actionable oncogenic drivers in individual tumors. Given the recent commercialization of the Theralink assay (TLA), knowledge gaps exist regarding its use in routine clinical practice and the impact of the test on clinical decision-making in real world practice. The primary objective of this analysis was to assess how the TLA has been integrated in therapy selection for breast cancer patients with a focus on understanding its target population, the rationale for patient selection by the treating physician, and the utilization of the molecule information generated by the assay as part of the therapeutic decision-making process. Findings from this study will help optimize patient selection and maximize the clinical impact of the test as a tool for advancing precision oncology. Methods: We prospectively collected data from 124 women with advanced breast cancer whose tumors were profiled using the Breast Cancer TLA from February, 2021 to May, 2022. All patients were confirmed as actively managed for advanced/recurrent breast cancer. Eight μm FFPE sections (n=5) from a recently collected tissue biopsy were used to isolate tumor epithelia via Laser Capture Microdissection and to generate RPPA-based molecular profiles. Clinical management and therapy selection information for 68 patients was gathered via surveys completed by treating physicians. Results: Median age of the 124 participants was 53 years (range 26-82) and 111 (89.5%) patients had stage IV disease. The cohort included 66 hormone receptors positive (of which 5 were HER2+), 51 triple negative, and 7 HR-/HER2+ breast cancers. The TLA yielded molecular information for all specimens and profiles were generated on average in 11 days. One or more targets were highly activated (highly actionable) in 91 patients (73.4%) and moderately activated (partially actionable) in 29 patents; only 4 patients had no actionable target (3.2%). Previous treatment information was available for 118 (95.2%) patients. The TLA was requested to assist with the selection of first-line treatment in 36 patients (of which 24 had previously received neoadjuvant treatment), second-line treatment in 35 patients and third- or subsequential-lines of treatment in 47 patients. Clinicians provided feedback on the use of the assay for 68 patients included in the study. The survey revealed that the TLA impacted treatment selection in 50 (73.5%) cases and was used to either expand options beyond standard of care (30 cases), refine/re-prioritize available treatments (11 cases), narrow treatment from a plethora of options (2 cases) or a combination of the three (7 cases). When TLA data were used for treatment selection, physicians defined the assay highly and moderately beneficial for patient management in 15 and 27 cases, respectively. Conclusion: Our study suggests the TLA yields useful information for selecting treatment for breast cancer patients with advanced/recurrent disease. In this prospective analysis, the assay identified actionable targets in more than 90% of patients, which is significantly higher than what has previously been reported for genomic profiling alone. Overall, physicians found the information yielded by the assay useful for selecting treatment. The inclusion of the TLA in oncology may offer important insights for advancing precision medicine for breast cancer patients. Citation Format: Kris Weinberg, Mariaelena Pierobon, Edik Blais, Justin Davis, Joyce O’Shaughnessy, Emanuel F. Petricoin. Impact of the Theralink CLIA protein/phosphoprotein assay on treatment selection in routine clinical practice: a prospective observational study in advanced breast cancer. [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P4-07-51.

Introduction/Background Endocrine therapy remains the fundamental treatment for advanced HR+ breast cancer (BC). For those patients who become refractory to endocrine therapy, resistance may be associated with mutations, amplifications, and fusions in the ESR1-encoded estrogen receptor. Here we examine the frequency of ESR1 alterations and the associated genomic landscape. Methods HR+/HER2- BC samples were sequenced with the OncomapTM ExTra assay, which uses whole-exome DNA sequencing with germline subtraction to detect somatic single nucleotide substitutions, indels, and copy number alterations (CNAs), and uses RNA sequencing to detect gene fusions. Tumor mutational burden (TMB) and microsatellite instability (MSI) are also reported. For analysis, BC samples were grouped by site: local (primary breast or regional lymph node) versus metastatic. Prior treatment history was unknown. Testing for a possible association between ESR1 and other biomarkers (genes, MSI, and TMB) was done using Fisher’s Exact Test (p≤0.05). Results A total of 988 HR+HER2- breast cancer patient samples were included in the analysis. Of these, 821 (83.1%) were local samples and the remaining 167 were metastatic samples, with liver (63, 37.7%), bone (20, 12.0%), skin (16, 9.6%) and chest wall (15, 9.0%) being the most common locations. ESR1 alterations were present in 84 tumor samples, 37 local and 47 metastatic, representing 4.5% and 28.1% of samples, respectively. ESR1 alterations included missense mutations (54 samples), fusions (29 samples), and amplifications (8 samples). The most common missense mutations were Y537S (20 samples, 37.0%), D538Q (20 samples, 37.0%), and E380Q (6 samples, 11.1%), which were located in the ligand binding domain and included both clonal and subclonal events. There were 30 ESR1 fusions identified, 17 (2.1%) in local and 13 in metastatic (7.7%) samples. Most fusions (24 samples, 82.8%) involved the same partner, CCDC170, while the other 6 fusions had unique partners. Examination of the 143 other biomarkers altered among ESR1-altered samples revealed 15 genes and MSI-high status that appeared to be over-represented (Table 1). However, none of the associations were statistically significant after correcting for multiple comparisons. Further, there was no evidence that the prevalence of ERBB2, TP53, AKT1 and PIK3CA alterations differed by ESR1 status (Table 1). Conclusions ESR1 alterations were significantly more common in HR+/HER2- metastatic breast cancer samples compared to local samples. Comprehensive genomic profiling with RNA sequencing identified both common and rare ESR1 fusions, which were most frequent in the metastatic samples. No significant difference in the molecular profile of ESR1 altered vs ESR1 wildtype samples was found in this cohort. Clinical trials with novel selective ER degraders (SERDs) to target these ESR1 alterations are ongoing. Table 1. Biomarkers that showed the highest association with ESR1 and other notable breast cancer biomarkers. Citation Format: Gargi Basu, Sameer S. Udhane, Susan Dombrowski, Lenny Hong, Fadel Alyaqoub, Michelle Barbi de Moura, Thiruppavai Chandrasekaran, Turgut Dogruluk, David Driscoll, Aimee Jalkanen, Pawan Noel, Szabolcs Szelinger, Min Wang, David Hall, Jess Hoag, Janine Lobello, Frederick Baehner, Snehal Thakkar, Joyce O’Shaughnessy. ESR1-alterations in HR+HER2- breast cancer patients [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P5-14-12.

Background: Only a subset of patients with metastatic triple-negative breast cancers (TNBC) demonstrate response to FDA approved PD-1 immune checkpoint blockade (ICB), and few have durable responses. Data suggests that breast cancers have defects in antigen presentation and that antigen presenting cells especially the DC1 subtype of dendritic cells (DCs) are required for response to ICB. CD40 agonists activate antigen presenting cells including DCs and B cells and also repolarize macrophages to an anti-tumor phenotype. Flt3 ligand is a growth factor that increases differentiation and expansion of DCs. We recently demonstrated in pre-clinical TNBC models that the combination of liposomal-doxorubicin chemotherapy, a CD40 agonist, and a Flt3 ligand improves outcomes compared to alternate combinations. Methods: This is a single arm phase I pilot study of liposomal-doxorubicin, CDX-1140 (CD40 agonist), and CDX-301 (Flt3 ligand) combination therapy in patients with metastatic or unresectable locally advanced metastatic TNBC. Patients will be randomized to 3 lead-in arms (triplet therapy, doublet immunotherapy only, or liposomal-doxorubicin only) for 1 cycle prior to receiving triplet therapy with fresh tissue biopsies before and after the lead-in treatment. CDX-301 will be discontinued after 2 cycles; liposomal-doxorubicin and CDX-1140 will be continued until disease progression or clinically limiting toxicities. Primary endpoint is determination of a recommended phase 2 dose based on treatment-related adverse events including dose-limiting toxicities. Secondary endpoints include anti-tumor immune response after triplet therapy, after immunotherapy alone, and after liposomal-doxorubicin alone; median progression-free survival, overall response rate, duration of response, and clinical benefit rate. Key eligibility criteria are unresectable stage III or stage IV TNBC (ER ≤10%, PR ≤10%, HER2/neu negative), 1st to 3rd line metastatic treatment setting (1st line patients need to be PD-L1 negative by 22C3 assay), measurable disease by RECIST 1.1 criteria, consent for pre-treatment and on-treatment biopsies of amenable soft tissue tumor lesions, no prior treatment with an anti-CD40 antibody or a Flt3 ligand, no anthracycline treatment in the metastatic setting, no prior progression while on anthracycline-based therapy or within 6 months of completing neoadjuvant chemotherapy, and no history of non-infectious pneumonitis or current pneumonitis. This trial will enroll up to 45 patients across multiple sites (NCT05029999). Citation Format: Sangeetha Reddy, Meredith Carter, Isaac Chan, Nisha Unni, Namrata Peswani, Dawn Klemow, Samira Syed, Shahbano Shakeel, Farjana Fattah, Chul Ahn, Yisheng Fang, Heather McArthur, Nicole Sinclair, Michael Yellin, Denise Yardley, Nan Chen, Joyce O’Shaughnessy, Rita Nanda, Suzanne D. Conzen, Carlos Arteaga. Phase 1 trial of anthracycline chemotherapy in combination with CD40 agonist and Flt3 ligand in metastatic triple-negative breast cancer [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr OT2-17-01.

Background: In early-stage triple-negative breast cancer (TNBC), there is accumulating evidence of a correlation between tumor-infiltrating lymphocytes in tumor tissue and favorable clinical outcomes, with a high CD8+/regulatory T-cell (Treg) ratio after neoadjuvant chemotherapy being predictive of overall survival and associated with pathologic complete response (Ladoire S, et al. Br J Cancer. 2011; Park YH, et al. Nat Commun. 2020). Trilaciclib is a transient inhibitor of cyclin-dependent kinase 4/6 that is administered intravenously prior to chemotherapy. In preclinical studies, trilaciclib has been shown to have immune-enhancing effects by differentially arresting CD8+ T-cell and Treg subsets, which is followed by the faster recovery of CD8+ T cells than Tregs in the tumor microenvironment. Methods: This phase 2, single-arm, open-label study aims to evaluate neoadjuvant, single-dose trilaciclib followed by trilaciclib plus dose-dense anthracycline/cyclophosphamide and taxane in patients with early-stage TNBC (NCT05112536). Patients with previously untreated, non-metastatic, confirmed TNBC and a primary tumor ≥ 1.5 cm of any nodal status receive a single dose of trilaciclib 240 mg/m2 during the lead-in phase, followed by 4 cycles of doxorubicin 60 mg/m2 plus cyclophosphamide 600 mg/m2, and 12 weekly cycles of paclitaxel 80 mg/m2. Trilaciclib 240 mg/m2 is administered prior to the first chemotherapy dose of each cycle. Pembrolizumab 400 mg every 6 weeks starting on day 1, cycle 1, and/or carboplatin AUC 1.5 every week starting on day 1, cycle 5, is allowed per investigator discretion. Tumor biopsies and peripheral blood samples are collected prior to any treatment, 7 days ± 1 day post administration of trilaciclib, and during surgery, with an additional blood sample collection on day 1, cycle 2. The primary objective is to evaluate the immune-based mechanism of action of trilaciclib after a single dose of trilaciclib, as measured by changes in the CD8+/Treg ratio in tumor tissue. Pathologic complete response, safety and tolerability, and additional exploratory immune biomarker endpoints will also be assessed. Results: As of June 3, 2022, 9 patients with early-stage TNBC had been enrolled and 8 patients had received the trilaciclib lead-in dose and initiated doxorubicin/cyclophosphamide. Patients had a median age of 53.0 years, and all had stage II tumors at diagnosis, with 7 having ductal carcinoma. The median number of chemotherapy cycles received was 3 (range 1–6), and all 8 patients received pembrolizumab. Seven patients continue study treatment; 1 patient discontinued due to disease progression. Five patients had an adverse event (AE) related to any study treatment, including 4 patients with ≥ 1 trilaciclib-related AE. There were no grade ≥ 3 treatment-related AEs or serious AEs. On-treatment, post-trilaciclib monotherapy biopsies were available for 4 patients. Following neoadjuvant trilaciclib treatment, the median density of stromal CD8+ T cells increased from 103.1/mm2 at baseline to 229.8/mm2 at day 7. The median CD8+/Treg ratio increased in 2 patients from 1.85 at baseline to 1.90 at day 7. Conclusions: Preliminary analysis of on-treatment tumor biopsies from 4 patients suggests that a single dose of trilaciclib may modulate the immune cell composition in the tumor microenvironment to support antitumor immune responses. The increase in CD8+ T cells following 7-day neoadjuvant treatment with trilaciclib supports previous data suggesting a role in T-cell infiltration. The complete dataset from all patients (estimated enrollment: N ≈ 24) and additional biomarker analyses will be presented. Citation Format: Michael Danso, Joyce O’Shaughnessy, Lisa S. Wang, Kailash Mosalpuria, Sara Hurvitz, Shom Goel, Sarah Ahn, Subing Cao, John S. Yi, Taofik Oyekunle, Amanda Jacobson, Andrew Beelen, Jeremy Force. Trilaciclib induces immune changes within the tumor microenvironment in early-stage triple-negative breast cancer [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P3-06-03.

Adjuvant abemaciclib plus endocrine therapy previously showed a significant improvement in invasive disease-free survival and distant relapse-free survival in hormone receptor-positive, human epidermal growth factor receptor 2 (HER2; also known as ERBB2)-negative, node-positive, high-risk, early breast cancer. Here, we report updated results from an interim analysis to assess overall survival as well as invasive disease-free survival and distant relapse-free survival with additional follow-up.In monarchE, an open-label, randomised, phase 3 trial, adult patients (aged ≥18 years) who had hormone receptor-positive, HER2-negative, node-positive, early breast cancer at a high risk of recurrence with an Eastern Cooperative Oncology Group performance status of 0 or 1 were recruited from 603 sites including hospitals and academic and community centres in 38 countries. Patients were randomly assigned (1:1) by means of an interactive web-based response system (block size of 4), stratified by previous chemotherapy, menopausal status, and region, to receive standard-of-care endocrine therapy of physician's choice for up to 10 years with or without abemaciclib 150 mg orally twice a day for 2 years (treatment period). All therapies were administered in an open-label manner without masking. High-risk disease was defined as either four or more positive axillary lymph nodes, or between one and three positive axillary lymph nodes and either grade 3 disease or tumour size of 5 cm or larger (cohort 1). A smaller group of patients were enrolled with between one and three positive axillary lymph nodes and Ki-67 of at least 20% as an additional risk feature (cohort 2). This was a prespecified overall survival interim analysis planned to occur 2 years after the primary outcome analysis for invasive disease-free survival. Efficacy was assessed in the intention-to-treat population. Safety was assessed in all treated patients. The study is registered with ClinicalTrials.gov, NCT03155997, and is ongoing.Between July 17, 2017, and Aug 12, 2019, 5637 patients were randomly assigned (5601 [99·4%] were women and 36 [0·6%] were men). 2808 were assigned to receive abemaciclib plus endocrine therapy and 2829 were assigned to receive endocrine therapy alone. At a median follow-up of 42 months (IQR 37-47), median invasive disease-free survival was not reached in either group and the invasive disease-free survival benefit previously reported was sustained: HR 0·664 (95% CI 0·578-0·762, nominal p0·0001). At 4 years, the absolute difference in invasive disease-free survival between the groups was 6·4% (85·8% [95% CI 84·2-87·3] in the abemaciclib plus endocrine therapy group vs 79·4% [77·5-81·1] in the endocrine therapy alone group). 157 (5·6%) of 2808 patients in the abemaciclib plus endocrine therapy group died compared with 173 (6·1%) of 2829 patients in the endocrine therapy alone group (HR 0·929, 95% CI 0·748-1·153; p=0·50). The most common grade 3-4 adverse events were neutropenia (in 548 [19·6%] of 2791 patients receiving abemaciclib plus endocrine therapy vs 24 [0·9%] of 2800 patients in the endocrine therapy alone group), leukopenia (318 [11·4%] vs 11 [0·4%]), and diarrhoea (218 [7·8%] vs six [0·2%]). Serious adverse events occurred in 433 (15·5%) of 2791 patients receiving abemaciclib plus endocrine therapy versus 256 (9·1%) of 2800 receiving endocrine therapy. There were two treatment-related deaths in the abemaciclib plus endocrine therapy group (diarrhoea and pneumonitis) and none in the endocrine therapy alone group.Adjuvant abemaciclib reduces the risk of recurrence. The benefit is sustained beyond the completion of treatment with an absolute increase at 4 years, further supporting the use of abemaciclib in patients with high-risk hormone receptor-positive, HER2-negative early breast cancer. Further follow-up is needed to establish whether overall survival can be improved with abemaciclib plus endocrine therapy in these patients.Eli Lilly.

In the KEYNOTE-355 (KN355) trial, pembrolizumab in combination with chemotherapy demonstrated superior efficacy and manageable safety compared with chemotherapy alone in patients with previously untreated locally recurrent inoperable and metastatic triple-negative breast cancer (mTNBC) with PD-L1 positive (Combined Positive Score [CPS]≥ 10) tumours. This study aimed to evaluate the clinical benefits and risks of pembrolizumab measured by quality-adjusted survival in the trial population.The study used data from the final analysis of KN355. The Quality-adjusted Time Without Symptoms of disease progression or Toxicity of treatment (Q-TWiST) analysis was used to compare treatments of pembrolizumab plus chemotherapy versus chemotherapy alone. Patients' survival time was partitioned into three health states - toxicity before disease progression (TOX), time without symptoms or toxicity before disease progression (TWiST), and relapse (REL). Utilities for these health states were estimated using EuroQol-5 Dimensions, 3 Levels (EQ-5D-3L) data collected in KN355. Q-TWiST was derived as the utility-weighted sum of the mean health state durations.Patients randomised to pembrolizumab plus chemotherapy had 3.7 months greater Q-TWiST (relative gain of 18%; P = 0.003) compared to those randomised to chemotherapy at the median follow-up of 44 months, and 4.3 months greater Q-TWiST (relative gain of 20%; P = 0.004) at the maximum follow-up of 52 months. The Q-TWiST gain increased with longer follow-up time.Pembrolizumab plus chemotherapy was associated with statistically significant and clinically important improvement in Q-TWiST compared to chemotherapy in previously untreated PD-L1-positive mTNBC.

PURPOSE: Somatostatin analogs octreotide long-acting release (octLAR) and lanreotide are equally acceptable in National Comprehensive Cancer Network guidelines for neuroendocrine tumors (NETs). Lanreotide is more expensive and given by deep subcutaneous injection, whereas octLAR is given intramuscularly. We evaluated patient preference between these agents in terms of injection site pain. MATERIALS AND METHODS: Randomized, single-blinded study. Patients with NETs received injections every 4 weeks. Arm 1: octLAR × 3, then lanreotide × 3; arm 2: reverse order. Self-reported injection site pain scores (range, 0-10) were obtained after each of the first three injections. Primary end point was comparison of mean pain scores over the first three injections. Secondary end points included patient-reported preference. RESULTS: Fifty-one patients enrolled (26 in arm 1 and 25 arm 2), all evaluable for primary end point. No significant difference was identified in the mean pain score over the first three injections (2.4 ± 1.9 v 1.9 ± 1.5, P = .5). Thirty-four of 51 (67%) patients (15 in arm 1 and 19 in arm 2) completed post-therapy questionnaires and were evaluable for secondary end points. Seven patients (47%) in arm 1 and eight patients (42%) in arm 2 indicated no drug preference at the end of treatment. In the other 19 patients, more patients indicated mild or strong preference for octLAR over lanreotide. CONCLUSION: We found minimal pain with octLAR and lanreotide and no significant pain score differences between the two. Patients indicating a drug preference trended toward favoring octLAR.

Purpose PI3K/AKT pathway alterations are frequent in hormone receptor-positive (HR+) breast cancers. IPATunity130 Cohort B investigated ipatasertib–paclitaxel in PI3K pathway-mutant HR+ unresectable locally advanced/metastatic breast cancer (aBC). Methods Cohort B of the randomized, double-blind, placebo-controlled, phase 3 IPATunity130 trial enrolled patients with HR+ HER2-negative PIK3CA/AKT1/PTEN-altered measurable aBC who were considered inappropriate for endocrine-based therapy (demonstrated insensitivity to endocrine therapy or visceral crisis) and were candidates for taxane monotherapy. Patients with prior chemotherapy for aBC or relapse 2, days 1, 8, 15), every 28 days until disease progression or unacceptable toxicity. The primary endpoint was investigator-assessed progression-free survival (PFS). Results Overall, 146 patients were randomized to ipatasertib–paclitaxel and 76 to placebo–paclitaxel. In both arms, median investigator-assessed PFS was 9.3 months (hazard ratio, 1.00, 95% CI 0.71–1.40) and the objective response rate was 47%. Median paclitaxel duration was 6.9 versus 8.8 months in the ipatasertib–paclitaxel versus placebo–paclitaxel arms, respectively; median ipatasertib/placebo duration was 8.0 versus 9.1 months, respectively. The most common grade ≥ 3 adverse events were diarrhea (12% with ipatasertib–paclitaxel vs 1% with placebo–paclitaxel), neutrophil count decreased (9% vs 7%), neutropenia (8% vs 9%), peripheral neuropathy (7% vs 3%), peripheral sensory neuropathy (3% vs 5%) and hypertension (1% vs 5%). Conclusion Adding ipatasertib to paclitaxel did not improve efficacy in PIK3CA/AKT1/PTEN-altered HR+ HER2-negative aBC. The ipatasertib–paclitaxel safety profile was consistent with each agent’s known adverse effects. Trial registration NCT03337724.

Background The burden of vancomycin-associated acute kidney injury (V-AKI) is unclear because it is not systematically monitored. The objective of this study was to develop and validate an electronic algorithm to identify cases of V-AKI, and to determine its incidence. Methods Adults and children admitted to one of five health system hospitals from January 2018 to December 2019 who received at least one dose of intravenous (IV) vancomycin were included. A subset of charts was reviewed using a V-AKI assessment framework to classify cases as unlikely, possible, or probable events. Based on review, an electronic algorithm was developed and then validated using another subset of charts. Percent agreement and kappa coefficients were calculated. Sensitivity and specificity were determined at various cutoffs, using chart review as the reference standard. For courses ≥48 hours, the incidence of possible or probable V-AKI events was assessed. Results The algorithm was developed using 494 cases and validated using 200 cases. The percent agreement between the electronic algorithm and chart review was 92.5% and the weighted kappa was 0.95. The electronic algorithm was 89.7% sensitive and 98.2% specific in detecting possible or probable V-AKI events. For the 11,073 courses of ≥48 hours of vancomycin among 8,963 patients, the incidence of possible or probable V-AKI events was 14.0%; the V-AKI incidence rate was 22.8 per 1,000 days of IV vancomycin therapy. Conclusions An electronic algorithm demonstrated substantial agreement with chart review and had excellent sensitivity and specificity in detecting possible or probable V-AKI events. The electronic algorithm may be useful for informing future interventions to reduce V-AKI.

PURPOSE For patients with hormone receptor–positive (HR+), human epidermal growth factor receptor 2–negative (HER2–) metastatic breast cancer (MBC), first-line treatment is endocrine therapy (ET) plus cyclin-dependent kinase 4/6 inhibition (CDK4/6i). After disease progression, which often comes with ESR1 resistance mutations (ESR1-MUT), which therapies to use next and for which patients are open questions. An active area of exploration is treatment with further CDK4/6i, particularly abemaciclib, which has distinct pharmacokinetic and pharmacodynamic properties compared with the other approved CDK4/6 inhibitors, palbociclib and ribociclib. We investigated a gene panel to prognosticate abemaciclib susceptibility in patients with ESR1-MUT MBC after palbociclib progression. METHODS We examined a multicenter retrospective cohort of patients with ESR1-MUT MBC who received abemaciclib after disease progression on ET plus palbociclib. We generated a panel of CDK4/6i resistance genes and compared abemaciclib progression-free survival (PFS) in patients without versus with mutations in this panel (CDKi-R[–] v CDKi-R[+]). We studied how ESR1-MUT and CDKi-R mutations affect abemaciclib sensitivity of immortalized breast cancer cells and patient-derived circulating tumor cell lines in culture. RESULTS In ESR1-MUT MBC with disease progression on ET plus palbociclib, the median PFS was 7.0 months for CDKi-R(–) (n = 17) versus 3.5 months for CDKi-R(+) (n = 11), with a hazard ratio of 2.8 ( P = .03). In vitro, CDKi-R alterations but not ESR1-MUT induced abemaciclib resistance in immortalized breast cancer cells and were associated with resistance in circulating tumor cells. CONCLUSION For ESR1-MUT MBC with resistance to ET and palbociclib, PFS on abemaciclib is longer for patients with CDKi-R(–) than CDKi-R(+). Although a small and retrospective data set, this is the first demonstration of a genomic panel associated with abemaciclib sensitivity in the postpalbociclib setting. Future directions include testing and improving this panel in additional data sets, to guide therapy selection for patients with HR+/HER2– MBC.

Background: CDK7 inhibition is a promising therapeutic strategy in cancer; acting as a regulator of the cell cycle, transcription and endocrine receptor signalling [1]. Patients with HR+BC post CDK4/6 inhibitor treatment have a poor prognosis; median progression free survival (mPFS) of ~ 8 weeks for fulvestrant post CDK4/6i in HR+BC [2,3]. Pre-clinical HR+BC models indicate the potential for synergy when the CDK7 inhibitor samuraciclib is combined with the Selective Estrogen Receptor Degrader fulvestrant [4]Materials and Methods: This single arm cohort assessed the tolerability and efficacy of samuraciclib in combination with standard dose fulvestrant in patients with advanced HR+BC; all patients had previously received an aromatase inhibitor and a CDK4/6i for advanced disease.Results: 31 patients with HR+BC received the combination of standard dose with fulvestrant and samuraciclib. 6 patients received samuraciclib dose of 240mg once daily (QD) and 25 patients a dose of 360mg QD. The combination treatment was generally well tolerated, with adverse drug reactions (AE) of note being G1-2 nausea, vomiting and diarrhoea; the majority of patients staying on treatment until disease progression.RECIST evaluation indicates evidence of reduction in tumor disease burden, including a partial response in one patient who has been on treatment for ~ 1 year.Graphic illustrations of data, including ‘waterfall’ and ‘swimmer’ plots, will be presented along with stratification data based on demographic factors such as hepatic involvement and cfDNA analysis (ESR1m, PI3Km).Conclusions: Samuraciclib has demonstrated an acceptable safety profile with evidence of anti-tumour activity in combination with fulvestrant for patients with advanced HR+BC who have progressed on their prior CDK4/6i.References:1.Patel et al., Mol Cancer Therap. 20182.Juric et al., SABCS 20183.Lindeman et al., JCO 20214.Jeselsohn et al., SABCS 2019 Citation Format: Charles Coombes, Sasha J Howell, Matthew G Krebs, Simon Lord, Laura M Kenny, Ash Bahl, Glen Clack, Edward Ainscow, Paul A Dickinson, Raluca Fostea, Janine Mansi, Carlo Palmieri, Gianflippo Bertelli, Rinath Jeselsohn, Zahi Mitri, William J Gradishar, Sagar Sardesai, Joyce O'Shaughnessy, Patrick Ward, Pavani Chalasani, Manfred Lehnert, Simak Ali, Stuart McIntosh. Study of samuraciclib (CT7001), a first-in-class, oral, selective inhibitor of CDK7, in combination with fulvestrant in patients with advanced hormone receptor positive HER2 negative breast cancer (HR+BC) [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr GS3-10.

Introduction: Overexpression of HER2 occurs in 15%-20% of early breast cancers (EBC) and is considered more aggressive than other types of breast cancer. Though HER2-targeted therapies have improved patient outcomes, up to 25% of patients will suffer relapse within 10 years, from which the majority of patients will die from incurable metastatic disease. Previous review articles have identified prognostic factors for recurrence for EBC, such as pathological complete response (pCR), hormone receptor (HR) status, and residual cancer burden (RCB). However, most of these were not specific for HER2+ EBC. The goal of this literature analysis was to confirm and identify patient and disease factors that correlate with recurrence in patients with HER2+ EBC. Methods: Primary research articles (inclusive of randomized controlled trials, retrospective cohort analyses, and database analyses) were identified using NCBI PubMed via the search criteria “HER2+ breast cancer,” followed by “early-stage” or “adjuvant” therapy, followed by “relapse” or “recurrence.” Search results were restricted to publications from 2019-2021 that were written in English to account for modern treatment options, including trastuzumab + pertuzumab, ado-trastuzumab emtansine, and neratinib. These same terms were applied to oncology abstracts presented at ASCO 2019-2021; ESMO 2019-2020; ESMO Breast 2019 and 2021; SABCS 2019 and 2020; and St Gallen 2019 and 2021. All results were analyzed for risk factors for recurrence associated with HER2+ EBC. Results: Using the search criteria, we identified 351 research articles, and listed conferences were searched for relevant abstracts. Of these, 53 journal articles and 57 abstracts that assessed risk factor terms, including “age at diagnosis,” “BMI,” “tumor size at diagnosis,” “lymph node status,” “hormone receptor status,” “pCR status,” “smoking history,” and/or “biomarkers,” were analyzed. These were evaluated individually, where possible. Various prognostic scoring methods were also evaluated for their ability to assess the risk factors of recurrence for HER2+ EBC. The RCB prognostic scoring system correlated most strongly to identifying EBC at risk of recurrence amongst all factors evaluated. We also confirmed the results of prior reviews listing non-pCR and fewer tumor-infiltrating lymphocytes (TILs) as risk factors for HER2+ EBC recurrence. HR status remained an important risk factor for recurrence, with HER2+/HR+ disease more likely to occur. In addition, patients with a lower BMI were more likely to have HR- EBC, but no conclusive relationship to risk of recurrence could be determined for BMI. Clinical factors including tumor size, involvement of ≥2 lymph nodes, and a younger age at diagnosis (≤50 years) were also risk factors for recurrence. Of the biomarkers identified, Ki67 represented the strongest association with recurrence. Further analyses of the risk factors identified by the literature review will be presented at the meeting. Conclusion: In this literature analysis, non-pCR, fewer TILs, HR status, younger age at diagnosis, and low Ki67 were identified as potential risk factors for HER2+ recurrence. Finally, RCB correlated strongly with a risk of progression in patients with HER2+ EBC. Patients who have these risk factors could potentially benefit from additional treatments for their early-stage disease in an effort to reduce their risk of recurrence. Citation Format: Joyce O'Shaughnessy, William Gradishar, Ruth O’Regan, Vijayakrishna Gadi. Assessment of risk factors for HER2+ breast cancer recurrence: A literature review [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P2-10-08.

BACKGROUND: Contemporary clinical trials of HER2-targeted therapies have shown benefits regarding recurrence and survival in patients (pts) with HER2+ early stage breast cancer. The outcomes of pts treated in community practice settings who had a pathologic complete response (pCR) to neoadjuvant therapy or who had residual disease at definitive surgery (non-pCR) have not been well characterized. This preliminary study aimed to describe the patient characteristics, disease-free survival (DFS) and overall survival (OS) in patients with and without pCR following neaoadjuvant HER2-targeted therapy in The US Oncology Network. METHODS: This retrospective cohort study identified pts diagnosed with stage I-III HER2+ breast cancer who initiated neoadjuvant HER2-targeted therapy in the community setting between April 1, 2014 - March 31, 2019. Pts were followed through the date of last visit, death, or study end (March 31, 2021), whichever occurred first. Data were collected from the US Oncology Network’s electronic medical record database, iKnowMed. Natural language processing/artificial intelligence was used to identify pts with pCR status and pts with disease recurrence during the study period. Patient profiles, risk of recurrence (RR), and time to recurrence (TTR) were assessed descriptively. Kaplan-Meier methods were used to evaluate DFS and OS from the start of neoadjuvant therapy. Results were stratified by pCR status. RESULTS: The study included 641 pts (median age, 55 years), 71% had non-pCR and 29% had pCR. The majority of pts were Caucasian (79%) or black (8%). At diagnosis, 78% of pts had stage I/II disease, and 21% stage III. Nearly 74% were HR+. With a median follow-up of 33 months, pts who had non-pCR had a higher risk of disease recurrence (10.3% vs 8.1%) and a shorter median TTR (18.6 vs 21.1 months) compared to pts with pCR. Three-year DFS (87.5% vs 92.2%) and OS (96.0% vs 98.8%) were lower in pts with non-pCR than with pCR. CONCLUSIONS:Findings from this real-world study of HER2+ early stage breast cancer pts who received neoadjuvant HER2-targeted therapy in the community setting suggested that pts with non-pCR had shorter DFS and OS outcomes than pts with pCR. Pts with non-pCR had a risk of recurrence of nearly 10% over approximately a 3-year time period . This residual risk of recurrence among non-pCR pts suggested a potential opportunity to improve long-term outcomes in this group. Future analyses, including HR subgroups, are planned as data mature and longer follow-up time is available. Results on additional pts with known pCR/non-pCR data, with longer follow-up, and outcomes by HR+ vs HR- status will be presented. Disclosure DeclarationThis study was funded by Puma Biotechnology, Inc. Outcomes of pts with pCR or non-pCR following neoadjuvant HER2-targeted therapyNon-pCRpCROverall CohortN=429N=185N=641Follow-up time, months, median (range)30.8 (0.0,81.6)38.4 (2.8,83.3)33.0 (0.0,83.3)Patients with recurrence, n (%)44 (10.3%)15 (8.1%)59 (9.6%)Time to recurrence, median (range)18.6 (0.0,42.4)21.1 (0.0,60.3)18.8 (0.0,60.3)Disease-free survival at 36 months87.5% (83.4,90.7)%92.2% (86.8,95.4)%89.0% (85.9,91.5)%Overall survival at 36 months96.0% (92.8,97.8)%98.8% (95.2,99.7)%97.0% (94.9,98.3)% Citation Format: Joyce O'Shaughnessy, Nina Oestreicher, Nicole Fulcher, Wan-Yu Tseng, April Beeks, Julia Moore, Deepa Lalla. Outcomes of patients with pathologic complete response following neoadjuvant HER2-targeted therapy in patients with HER2+ early stage breast cancer [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P3-12-20.

Background: Alpelisib (PIQRAY®) in combination with fulvestrant was approved by the US- FDA in May of 2019 for patients with hormone receptor-positive (HR+) and human epidermal growth factor receptor 2-negative (HER2-) PIK3CA mutant advanced or metastatic breast cancer (aBC or mBC) following progression on aromatase inhibitors. Prior to the US-FDA approval of alpelisib, routine molecular profile testing for this patient population was not supported by NCCN guidelines. Thus, data on the natural history of HR+/HER2- mBC patients, particularly in terms of biomarker testing and treatment patterns in a real-world patient setting, are limited. To understand integration of alpelisib into clinical practice for this patient population, this retrospective non-interventional study assessed biomarker testing, treatment patterns, and patient characteristics for patients at Texas Oncology (TxO) from 2015 to 2020.Methods: The study index date was defined as the first date of a new diagnosis of advanced BC (de novo or recurred mBC) between January 2015 and June 2020 with a minimum follow-up opportunity of 6 months follow-up. Treatment patterns were assessed until December 2020, allowing assessment of alpelisib real-world utilization post the US-FDA approval. Databases curated included the EMR (iKM), the TxO Precision Medicine (PM) Molecular databases. Information mined included total number of mBC patients, HR and HER2 status, and the presence and classification of PIK3CA mutations. Treatment patterns were also examined. Results: Study cohort consisted of 1093 patients for whom PIK3CA, HR, HER2 status and systemic treatment were known. Of these, 768 (70%) were HR+/HER2-, 220 (20%) were HR-/Her2HER2-, 73 (7%) were HR+/Her2HER2+ and 32 (3%) were HR-/Her2HER2+. Among all subtypes, 410 (38%) were PIK3CA mutant, and within HR+/HER2- cohort, 333 (43%) were PIK3CA mutant. Of the 105 patients treated with alpelisib, 102 (97%) were treated after drug approval, and the remaining 3 patients (3%) received alpelisib via compassionate use program. Within the HR+/HER2-/PIK3CA mutant patient cohort (n=333), 97 (29%) were treated with alpelisib. The most frequent alpelisib-containing regimen is alpelisib+fulvestrant, given to 84 (87%) of patients. It is most frequently given as a second- (n=28, 29%), third- (n=16, 16%) and fourth-line (n=16, 16%) lines of therapy. Out of 97 patients, 69 (71%) were treated previously with a cyclin-dependent kinase 4/6 inhibitor. The median duration of alpelisib therapy was 4.6 months. As of December 30, 2020, 34 of the 97 patients had treatment with alpelisib ongoing, 24 expired, 14 were referred to hospice,18 completed last recorded line of therapy prior to study end date, and 7 patients progressed to the next line of therapy. There was no noteworthy difference in patients treated vs. not treated with alpelisib with respect to age (mean 61.5 vs. 59.3 yrs.) or performance status (Karnofsky) (29% vs. 25% at 100%, 42% vs. 49% at 90% respectively). In PIK3CA mutant cancers, the most frequent PIK3CA mutations were H1047R, E545K, E542K, N345K and H1047L, and 43 (10%) had 2 or more mutations. Patient outcomes including the median progression free survival was also determined for this cohort and will be reported. Conclusions: This retrospective study demonstrates that 38% of mBC patients’ cancers across all sub-types harbored a PIK3CA mutation where multiple testing platforms were utilized in the community setting. Approximately 30% of patients with HR+/HER2-/PIK3CA mutant status did receive alpelisib. Co-morbidities and other clinically relevant factors between PIK3CA mutant patients who did and did not receive alpelisib, such as those on oral diabetes medication, insulin or had elevated HgbA1c, should be studied further. Citation Format: Joyce O'Shaughnessy, MD, Steven Paulson, MD, Lorraine Brisbin, M.S, James Lindsey, Anna Williford, Ph.D, Monica Lisi, Rohan C. Parikh, Ph.D, Stacey Simmons, MD and Sanjeev Balu, Ph.D. A real-world assessment of PIK3CA testing and alpelisib treatment patterns among metastatic breast cancer patients in a community oncology setting [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P5-13-16.

Background: In ASCENT, patients with mTNBC refractory to or relapsing after ≥2 prior chemotherapies (at least one in the metastatic setting) were randomized 1:1 to receive sacituzumab govitecan (SG) or single-agent treatment of physician’s choice (TPC) (capecitabine, eribulin, vinorelbine, or gemcitabine). Primary endpoint was progression free survival. Secondary endpoints included overall survival, objective response rate, clinical benefit rate, and safety. Here we examined whether health-related quality of life (HRQoL) differed by clinical response. Methods: The European Organization for Research and Treatment of Cancer Quality of Life Questionnaire (EORTC QLQC30) version 3 was used to assess HRQoL at baseline and on day 1 of each treatment cycle. This analysis included intention-to-treat patients who had a completed at least one of the 15 domains/scales at baseline and at least one evaluable assessment at post-baseline visits based on EORTC QLQ-C30. Patients were classified as responders (partial or complete disease response) or non-responders (stable or progressive disease or not evaluable) based on best overall response (RECIST). A mixed-effect model for repeated measures (MMRM) was used to estimate leastsquare (LS) mean EORTC QLQC30 score changes from baseline using all HRQoL data assessed during Cycle 2 Day 1 (C2D1) to C6D1 (where n was ≥25 in both treatment arms) for responders and nonresponders within each treatment group. Results: Mean QLQ-C30 subscale scores at baseline were similar between treatment arms. The analysis included 236 patients in the SG arm of the full trial population, of whom 82 (35%) were clinical responders; and 183 in the TPC arm, of whom 11 (6%) were clinical responders. Due to the small number of TPC responders, inferential statistical testing to compare between-group difference was not performed.Irrespective of their clinical response status, patients treated with SG showed more favorable LS mean changes than patients who received TPC in all EORTC QLQ-C30 domains, except for nausea/vomiting and diarrhea (Table). Overall, LS mean changes in EORTC QLQ-C30 scores in SG nonresponders were less favorable than those in SG responders, but more favorable than those in TPC responders and TPC nonresponders for most EORTC QLQ-C30 domains. Conclusions: The analysis demonstrates that regardless of response status, SG responders and non-responders showed a better trend in HRQoL changes than TPC. Patients who achieved a tumor response to SG may benefit most in HRQoL. Although patients treated with SG reported higher rates of diarrhea, this did not generate a negative impact on their overall quality of life or functioning. Table: Mixed effects model least-square mean EORTC QLQ-C30 score changes from baselineLeast-square mean change from baseline (95% confidence interval)SG responders(N=82)SG nonresponders(N=154)TPC responders(N=11)TPC non-responders(N=172)Global health status/QoL2.46 (-1.52, 6.43)-0.57 (-3.68, 2.54)-1.64 (-10.22, 6.95)-2.29 (-5.63, 1.05)FunctioningPhysical2.93 (-0.92, 6.79)0.22 (-2.71, 3.15)-3.47 (-11.93, 4.99)-3.75 (-6.87, -0.63)Role-0.35 (-5.74, 5.04)-3.23 (-7.45, 0.99)-8.40 (-19.93, 3.13)-7.33 (-11.88, -2.78)Emotional6.20 (2.23, 10.18)1.97 (-1.12, 5.06)4.87 (-3.70, 13.44)0.08 (-3.24, 3.40)Cognitive0.90 (-2.99, 4.79)-2.25 (-5.26, 0.76)-4.46 (-12.87, 3.95)-1.26 (-4.49, 1.98)Social2.06 (-3.50, 7.61)-3.35 (-7.65, 0.95)-5.79 (-18.29, 6.72)-4.36 (-8.99, 0.27)SymptomsFatigue0.90 (-3.49, 5.28)2.84 (-0.60, 6.29)4.15 (-5.34, 13.65)6.65 (2.93, 10.38)Nausea/vomiting4.68 (1.42, 7.95)4.03 (1.42, 6.64)1.38 (-5.53, 8.29)2.62 (-0.21, 5.45)Pain-11.40 (-16.43, -6.36)-8.57 (-12.48, -4.66)-11.99 (-22.85, -1.13)-0.24 (-4.47, 3.99)Dyspnea-7.88 (-13.09, -2.67)-1.90 (-5.93, 2.13)1.97 (-9.33, 13.27)3.86 (-0.47, 8.18)Insomnia-6.12 (-11.99, -0.26)-3.51 (-8.04, 1.02)4.83 (-7.85, 17.51)-0.98 (-5.86, 3.90)Appetite loss0.22 (-5.25, 5.70)5.45 (1.15, 9.75)8.67 (-3.05, 20.40)4.60 (-0.05, 9.26)Constipation0.93 (-4.57, 6.43)2.20 (-2.09, 6.49)3.87 (-7.96, 15.70)3.52 (-1.12, 8.16)Diarrhea16.03 (10.32, 21.74)13.65 (9.19, 18.11)2.46 (-9.88, 14.80)-1.53 (-6.34, 3.29)Financial difficulties-3.57 (-8.54, 1.39)-2.44 (-6.21, 1.34)-4.41 (-15.27, 6.46)0.61 (-3.42, 4.64)A higher score for a functional domain represents a higher or healthier level of functioning; a higher score for the global health status/QoL represents a higher overall HRQoL; but a higher score for a symptom domain represents a higher level of symptomatology or problems Citation Format: Sibylle Loibl, Sara M. Tolaney, Kevin Punie, Mafalda Oliveira, Hope S. Rugo, Aditya Bardia, Sara A. Hurvitz, Adam Brufsky, Kevin M Kalinsky, Javier Cortes, Joyce O’Shaughnessy, Lisa A. Carey, Luca Gianni, Véronique Diéras, Ling Shi, Mahdi Gharaibeh, Luciana Preger, Lee Moore, See Phan, Martine Piccart. Assessment of health-related quality of life by clinical response from the phase 3 ASCENT study in metastatic triple-negative breast cancer (mTNBC) [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P5-16-01.

Background: Hormone receptor-positive (HR+) is the most common molecular subtype of breast cancer accounting for approximately 2 out of every 3 patients. Adjuvant anti-estrogen therapy is the cornerstone of systemic therapy, underscoring the critical role of endocrine treatment which affects the majority of women with breast cancer. Furthering efforts to better understand endocrine response and resistance and implementing genomic tools to help individualize patient selection for endocrine therapy are of ongoing importance to improve outcomes. Breast Cancer Index (BCI) is a gene expression signature composed of the Molecular Grade Index (MGI) and HOXB13/IL17BR (H/I) that predicts the likelihood of extended endocrine benefit and quantifies the risk of both late (5-10 years) and overall (0-10 years) distant recurrence. BCI has recently been incorporated into the NCCN clinical practice guideline as a biomarker for prediction of benefit from extended endocrine therapy in patients with early-stage, HR+ breast cancer. The objective of the BCI Registry Study is to collect real-world evidence at a national level aimed at advancing patient care and optimizing duration of endocrine treatment and will be conducted in two phases. First, long-term patient outcomes and the impact of BCI on decision-making based on physician and patient reported outcomes as well as medication adherence to extended endocrine therapy will be assessed. Secondly, individual patient data on over 40 clinical variables will be collected and partnered with molecular profiling and genomic data for each patient to enable correlative analysis and novel biomarker research of endocrine sensitivity and resistance. Study Description: The BCI Registry Study is a prospective, multi-center, observational data registry and biospecimen repository for stage I-III HR+ breast cancer patients. The main objective of the Registry Study is prospective characterization of BCI predictive and prognostic performance. The primary endpoint is time to distant recurrence (TTDR), defined as the interval between the time of BCI testing and the first metastasis at distant organs. Secondary endpoints include time to any recurrences and medication adherence score over time. Eligibility criteria includes confirmed diagnosis of HR+ early-stage invasive breast carcinoma (ductal, lobular, or mixed ductal/lobular), either HER2 negative or positive and either node-negative or node-positive tumors with 1-3 positive lymph nodes (N1). Patients must have completed 4 to 7 years of primary adjuvant endocrine therapy and have pre-treatment tumor tissue available from a previous breast surgery or biopsy. Both physicians and patients will complete a pre- and post-test Decision Impact Questionnaire to assess the impact of BCI results on extended endocrine therapy decision-making. Patients who elect to complete 10 years of endocrine therapy will answer a Medication Adherence Questionnaire during annual follow-up visits. Follow-up of patients will end 10 years from initial breast cancer diagnosis. The Registry plans to enroll approximately 3,000 patients across approximately 40 study sites in the United States. Enrollment for the study began in Q2 2021, and 324 patients have been enrolled as of July 2021. For more information, please visit the ClinicalTrials.gov registration: NCT04875351. Citation Format: Joyce A O'Shaughnessy, Jenny R Fox, Carlos A Encarnación, Brandon O'Neal, Kai Treuner, Tara Sanft, Rachel C Jankowitz, Mark D Pegram, Catherine A Schnabel, Sami G Diab. The Breast Cancer Index registry study: A prospective multi-center observational study to evaluate patient outcome, clinical impact, and medication adherence in HR+ breast cancer patients considering treatment with extended endocrine therapy [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr OT1-10-01.

Introduction: It is well established that multidisciplinary tumor boards improve the decision-making process for cancer patients. Tumor boards have been shown to improve the accuracy of diagnosis and staging, optimize patient outcomes, increase adherence to guidelines, and educate our peers and trainees. However, over 80% of patients in the United States receive their cancer care in the community setting, where access to multi-disciplinary tumor boards may not be readily available. This may particularly impact underserved populations who often lack the resources to travel to an academic center for second opinions or treatment. The problem is worse in low-resource countries. Virtual expert tumor boards could provide an effective solution. Methods: Preeminent breast oncology faculty from around the Unites States were assembled into virtual tumor board panels via an online platform to discuss challenging cases submitted by community providers and trainees. These tumor boards consisted of a moderator, a breast radiologist, a breast medical oncologist, a breast surgeon, and a breast radiation oncologist. The purpose of this ongoing endeavor is to educate community oncologists on how to best manage challenging cases. Following tumor board discussions, written recommendations were shared with submitting providers within 48 hours and recordings of the discussions were also later provided. After submitting providers watched the recording of their case discussion, we conducted a survey to determine their perceived benefit of the expert panel discussion. Results: From Sept 2020 to June 2021, ten breast cancer panels were virtually convened with 17 expert faculty panelists. During that time, 21 providers submitted 94 cases from the U.S. and around the world to be discussed by the expert panel. Thirty-three percent of the providers who submitted a case to be discussed have subsequently submitted an additional case to a later panel. Surveys were sent to all submitting providers and responses were recorded from 16/21 submitters (76.2%). Conclusion: With more than three out of four submitters responding, we learned that not only is it feasible to convene virtual expert breast tumor boards to discuss challenging cases, but the vast majority of respondents learned new information, changed management of their patients, and wanted to submit additional cases. This effort could raise the level of breast cancer care around the world. Ongoing assessment of educational and patient care impacts will be necessary. QuestionNumber answered (n)Number who answered yes (%)Number who answered no (%)Did you learn something new from the PrecisCa discussion of your case scenario?1614 (87.5)2 (12.5)Will anything you learned from the PrecisCa discussion of your case scenario change the management of this or future patients?1615 (93.8)1 (6.2)Are you likely to submit a future challenging case scenario to PrecisCa?1616 (100)0 (0) Citation Format: Naomi Dempsey, Lauren Chiec, Mikala Lodder, Erin Shonkwiler, Kayla Haines, Reshma Mahtani, William Gradishar, Thomas Buchholz, Anne O'Dea, Norman Wolmark, Sara Hurvitz, Joyce O'Shaughnessy, Maxine Jochelson, Reni Butler, Eleftherios Mamounas, Frank Vicini, Mark Pegram, Chirag Shah, Tari King, Ruth O'Regan, Monica Morrow, Mohammad Jahanzeb. Raising the level of cancer care around the world: The feasibility and perceived benefit of a virtual breast tumor board [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P3-17-03.

Background: In contrast to the IMpassion130 trial evaluating atezo + nab-pac [Schmid, NEJM 2018], the randomized phase 3 IMpassion131 trial (NCT03125902) did not demonstrate significantly improved progression-free survival (PFS; primary endpoint) and showed no improvement in overall survival (OS; secondary endpoint) with the addition of atezo to pac as first-line therapy for mTNBC in either the PD-L1+ or the intention-to-treat (ITT) population [Miles, Ann Oncol 2021]. In IMpassion130, enhanced PFS and OS improvement with atezo + nab-pac were seen in the basal-like immune-activated (BLIA) subtype, whereas potential resistance to atezo + nab-pac was observed in the luminal androgen receptor (LAR) subtype [Emens, ASCO 2021]. LAR may be more prevalent in Asian populations [Ding, Oncotarget 2019], which represented one-third of patients enrolled in IMpassion131 and could have influenced the overall result. PFS outcomes were numerically worse in Asian vs non-Asian subgroups in IMpassion131 [Miles, Ann Oncol 2021]. To investigate potential reasons for observing different effects in IMpassion130 and IMpassion131, we explored the prevalence and impact on clinical outcomes of TNBC molecular subtypes and race in IMpassion131. Patients and Methods: Patients with mTNBC (no prior systemic therapy or ≥12 months since [neo]adjuvant chemotherapy) were randomized 2:1 to atezolizumab 840 mg or placebo (days 1, 15), both with paclitaxel 90 mg/m2 (days 1, 8, 15), every 28 days until disease progression or unacceptable toxicity, stratified by tumor PD-L1 status, prior taxane, liver metastases, and geographic region. Molecular subtypes according to Burstein classification were determined by RNA sequencing (Illumina TruSeq RNA Access) of baseline tumor samples. Prevalence of Burstein molecular subtypes [Burstein, Clin Cancer Res 2015] was assessed in Asian (of whom 69% were enrolled in China) and non-Asian populations; clinical outcomes were assessed according to molecular subtype and race using Cox proportional hazards analysis. All analyses were performed using the final data cut-off (Sep 4, 2020; median follow-up duration: 14.4 months). Results: The biomarker-evaluable population (BEP; n=471) was representative of the ITT population (n=651) with respect to baseline characteristics and PFS hazard ratio (HR; 0.75 [95% CI 0.61-0.92] vs 0.81 [95% CI 0.68-0.96], respectively). Distribution of molecular subtypes in the BEP was: 30% BLIA, 41% basal-like immune suppressed (BLIS), 24% LAR, 5% mesenchymal (MES), similar to IMpassion130. Among the BLIA samples, 82% were PD-L1+ and 18% PD-L1-; corresponding percentages were 41% vs 59% for BLIS, 31% vs 69% for LAR, and 32% vs 68% for MES. Compared with non-Asian patients, the Asian subgroup (n=117) included more LAR (31% vs 22%) and fewer MES (1% vs 6%) samples; this was particularly pronounced in the cohort enrolled in China (n=79; 37% LAR, 0% MES). PFS was improved with atezo + pac in the BLIA subtype (HR 0.66, 95% CI 0.45-0.97). None of the Burstein subgroups derived OS benefit from atezo + pac. Findings were similar irrespective of PD-L1 status. Direction of effect for PFS and OS favored the placebo + pac arm in the LAR Asian subgroup (n=30). Conclusion: In these exploratory analyses, the distribution of molecular subtypes and enhanced effect of atezo + pac in the BLIA subtype are consistent with findings from IMpassion130. The lack of improved efficacy with the combination of atezo + pac in the IMpassion131 trial cannot be explained by overrepresentation of a Burstein subtype less sensitive to atezo in the trial population. Citation Format: Fabrice André, Regula Deurloo, Aditi Qamra, David Cameron, Joseph Gligorov, Andreas Schneeweiss, Carlos Barrios, Binghe Xu, Ching-Wei Chang, Luciana Molinero, Shilpen Patel, Andrea Liptrot, Leilani Morales, David Miles, Joyce O’Shaughnessy. Activity of atezolizumab (atezo) plus paclitaxel (pac) in metastatic triple-negative breast cancer (mTNBC) according to Burstein molecular subtype: Analysis of the IMpassion131 trial [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr PD10-05.

Background: The estrogen receptor (ER) is the key therapeutic target for ER-positive (ER+), human epidermal growth factor receptor 2-negative (HER2-) breast cancer. Novel degraders of ER may overcome resistance to available endocrine therapy (ET) while providing consistent oral bioavailability and convenience of administration. LY3484356 is a novel, orally bioavailable selective estrogen receptor degrader (SERD) with pure antagonistic properties resulting in sustained inhibition of ER-dependent gene transcription and -cell growth. In the phase 1a/b EMBER trial, LY3484356 monotherapy demonstrated a favorable safety profile with pharmacokinetic (PK) exposures that exceeded fulvestrant. LY3484356 also showed single agent efficacy in patients with ER+, HER2- metastatic breast cancer (MBC), including in patients with baseline ESR1 mutations and fulvestrant- and/or CDK4/6 inhibitor- refractory disease1. Trial Design: EMBER-3 is a randomized, open-label, global phase 3 study comparing LY3484356 versus investigator’s choice of ET (fulvestrant or exemestane), in patients with ER+, HER2- locally advanced or MBC. Approximately 500 patients will be randomized 1:1 to receive LY3484356 (400 mg PO QD continuously in 28-day cycles) or investigator’s choice of ET (dosed per label). Males and pre-menopausal women will receive concomitant treatment with a GnRH agonist. Eligibility criteria: Eligible patients are adult males and females (pre- or post-menopausal) with ER+, HER2- locally advanced or MBC who have received prior treatment with an aromatase inhibitor, alone or in combination with a CDK4/6 inhibitor. No other prior therapy for advanced disease is permitted. Patients must have evaluable disease (measurable or non-measurable bone only). Study endpoints: The primary endpoint is investigator-assessed progression-free survival (PFS) per RECIST v1.1. Secondary endpoints include BIRC-assessed PFS, overall survival, objective response rate, duration of response, clinical benefit rate, safety and tolerability, PK and patient reported outcomes. Recruitment for the EMBER-3 study begins in Q3 2021. Reference: 1Jhaveri et al. J Clin Oncol 2021 39:15_suppl, 1050 Citation Format: Komal Jhaveri, Nadia Harbeck, Philippe Aftimos, Sung-Bae Kim, Xavier Pivot, Cristina Saura, Giuseppe Curigliano, Monica Casalnuovo, Xuejing Aimee Wang, Suzanne R.L. Young, Lillian Smyth, Joyce O'Shaughnessy. EMBER-3: A randomized phase 3 study of LY3484356, a novel, oral selective estrogen receptor degrader vs investigator’s choice of endocrine therapy of either fulvestrant or exemestane, in patients with estrogen receptor-positive, human epidermal growth factor receptor 2-negative, locally advanced or metastatic breast cancer previously treated with endocrine-based therapy [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr OT2-11-01.

Background: SG is an antibody-drug conjugate composed of an anti-Trop-2 antibody coupled to the cytotoxic SN-38 payload via a proprietary, hydrolyzable linker. SG is FDA approved for pts with mTNBC who received ≥2 prior chemotherapies (≥1 in the metastatic setting). The confirmatory phase 3 ASCENT study (NCT02574455) in pts treated in second line or greater (2L+) mTNBC demonstrated significant progression-free survival (PFS) and overall survival (OS) benefit of SG over single-agent chemotherapy treatment of physician’s choice (median PFS: 4.8 vs 1.7 months, HR 0.43, P Citation Format: Javier Cortés, Aditya Bardia, Delphine Loirat, Sara M. Tolaney, Kevin Punie, Mafalda Oliveira, Sara A. Hurvitz, Adam Brufsky, Sagar Sardesai, Kevin M Kalinsky, Tiffany Traina, Erika Hamilton, Joyce O’Shaughnessy, Véronique Diéras, Lisa A. Carey, Martine Piccart, Sibylle Loibl, Hope S. Rugo, Yanni Zhu, See Phan, Luca Gianni. Post-progression therapy outcomes in patients (pts) from the phase 3 ASCENT study of sacituzumab govitecan (SG) in metastatic triple-negative breast cancer (mTNBC) [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P5-16-15.

Targeting the androgen receptor (AR) may be the next important endocrine therapy for women with advanced breast cancer. AR is the most abundantly expressed steroid receptor in breast cancer and has been demonstrated to be a tumor suppressor when activated. Enobosarm is an oral selective nonsteroidal agonist that activates the AR in breast cancer. Enobosarm has an extensive clinical experience in 25 clinical trials and 1,450 dosed subjects including in breast cancer where three Phase 2 studies have been conducted two of which were in women (158 subjects) who had AR+/ER+/HER2- metastatic breast cancer (MBC).The larger Phase 2 clinical trial (G200802) evaluated 9mg and 18mg enobosarm daily oral dosing in 136 women with ER+/HER2- MBC who previously responded to endocrine treatment. Patients were heavily pretreated having progressed on an average of 3 endocrine treatments and 90% had prior chemotherapy. Enobosarm showed efficacy activity in the overall study with a clinical benefit rate at 6 months of 32% (95% CI: 19.5%,46.7%) for the 9 mg and 29% (95% CI: 17.1%,43.1%) for the 18 mg evaluable cohorts. Quality of life assessments showed significant improvement from baseline for both enobosarm cohorts (p=0.002). Enobosarm was well tolerated at both doses. In a post-hoc analysis in all patients (9mg and 18mg) with known AR status and measurable disease (n=84), AR expression in breast. cancer tissue (%AR nuclei staining) correlated with efficacy outcomes. When comparing AR nuclei staining ≥40% (n=47) compared to patients with an AR nuclei staining Citation Format: Adam Brufsky, Hannah Linden, Hope Rugo, Charles Vogel, Joyce A O'Shaughnessy, Robert H Getzenberg, K. Gary Barnette, Domingo Rodriguez, Mitchell S Steiner, Erica Mayer. Randomized, multicenter, international phase 3 ARTEST study to evaluate the efficacy and safety of enobosarm versus active control for the treatment of AR+ ER+ HER2- metastatic breast cancer in patients who progressed on a nonsteroidal aromatase inhibitor, fulvestrant and CDK 4/6 inhibitor [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr OT2-17-01.

Background Selective estrogen receptor degraders (SERDs) block estrogen receptor (ER) associated signaling and have created interest for treating patients (pts) with advanced ER+ breast cancer (BC). Fulvestrant is currently the only SERD available for advanced BC but requires intramuscular administration, limiting the applied dose, exposure and receptor engagement. Amcenestrant (SAR439859) is an oral SERD that binds with high affinity to both wild-type and mutant ER, blocking estradiol binding and promoting up to 98% ER degradation in preclinical studies. In the phase I AMEERA-1 study of pretreated pts with ER+/HER2- advanced BC, amcenestrant 150-600 mg once daily (QD) showed a mean ER occupancy of 94% with plasma concentrations > 100 ng/mL and a favorable safety profile (Bardia, 2019; data on file). Combination therapy with amcenestrant + palbociclib (palbo) was also evaluated as part of this ongoing phase I study. CDK 4/6 inhibitors (CDK4/6i) combined with an aromatase inhibitor (AI), the gold standard for first line treatment for advanced breast cancer, prolong progression free survival (PFS) in pts with no prior treatment for ER+/HER2- advanced BC, but OS benefit has not been shown yet in postmenopausal pts. There remains a clinical need for more effective treatments in this setting. Methods AMEERA-5 (NCT04478266) is an ongoing, prospective, randomized, double-blind phase III study comparing the efficacy and safety of amcenestrant + palbo with that of letrozole + palbo in pts with advanced, locoregional recurrent or metastatic ER+/HER2- BC who have not received prior systemic therapy for advanced disease. The study includes men, pre/peri-menopausal (with goserelin) and post-menopausal women. Pts with progression during or within 12 months of (neo)adjuvant endocrine therapy using any of the following agents are excluded: AI, selective estrogen receptor modulators, CDK4/6i. Pts are randomized 1:1 to either continuous amcenestrant 200 mg or letrozole 2.5 mg QD orally with matching placebos; both combined with palbo 125 mg QD orally (d1-21 every 28-d cycle). Randomization is stratified according to disease type (de novo metastatic vs recurrent disease), the presence of visceral metastasis, and menopausal status. The primary endpoint is investigator assessed progression free survival (PFS) (RECIST v1.1). Secondary endpoints are overall survival, PFS2, objective response rate, duration of response, clinical benefit rate, pharmacokinetics of amcenestrant and palbo, health-related quality of life, time to chemotherapy, and safety. Biomarkers will be measured in paired tumor biopsies and cell free deoxyribonucleic acid (cfDNA) over time. Target enrolment = 1066 pts; enrolment as of 6/2021 = 415 pts. Bardia A, et al., J Clin Oncol. 2019; 37 (15 suppl):1054. Funding: Sanofi. This abstract was accepted and previously presented at the 2021 American Society of Clinical Oncology Annual Meeting. All rights reserved. Citation Format: Aditya Bardia, Javier Cortes, Sara Hurvitz, Suzette Delaloge, Hiroji Iwata, Zhi-Ming Shao, Dheepak Kanagavel, Patrick Cohen, Qianying Liu, Sylvaine Cartot-Cotton, Vasiliki Pelekanou, Joyce O’Shaughnessy. AMEERA-5 : A randomized, double-blind phase 3 study of amcenestrant (SAR439859) + palbociclib versus letrozole + palbociclib for previously untreated ER+/HER2- advanced breast cancer [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr OT2-11-08.

Purpose In MONARCH 1 (NCT02102490), single-agent abemaciclib demonstrated promising efficacy activity and tolerability in a population of heavily pretreated women with refractory HR+, HER2− metastatic breast cancer (MBC). To help interpret these results and put in clinical context, we compared overall survival (OS) and duration of therapy (DoT) between MONARCH 1 and a real-world single-agent chemotherapy cohort. Methods The real-world chemotherapy cohort was created from a Flatiron Health electronic health records-derived database based on key eligibility criteria from MONARCH 1. The chemotherapies included in the cohort were single-agent capecitabine, gemcitabine, eribulin, or vinorelbine. Results were adjusted for baseline demographics and clinical differences using Mahalanobis distance matching (primary analysis) and entropy balancing (sensitivity analysis). OS and DoT were analyzed using the Kaplan–Meier method and Cox proportional hazards regression. Results A real-world single-agent chemotherapy cohort (n = 281) with eligibility criteria similar to the MONARCH 1 population (n = 132) was identified. The MONARCH 1 (n = 108) cohort was matched to the real-world chemotherapy cohort (n = 108). Median OS was 22.3 months in the abemaciclib arm versus 13.6 months in the matched real-world chemotherapy cohort with an estimated hazard ratio (HR) of 0.54. The median DoT was 4.1 months in MONARCH 1 compared to 2.9 months in the real-world chemotherapy cohort with HR of 0.76. Conclusions This study demonstrates an approach to create a real-world chemotherapy cohort suitable to serve as a comparator for trial data. These exploratory results suggest a survival advantage and place the benefit of abemaciclib monotherapy in clinical context.

Background: The Breast Cancer Index (BCI) is a validated gene expression assay that provides a quantitative individualized risk of late recurrence and predicts the likelihood of benefit from extended endocrine therapy (EET) in HR+ early-stage breast cancer. The objective of this analysis was to assess the impact of BCI on clinical decision-making regarding EET in the BCI Registry Study. Methods: The BCI Registry Study is an ongoing, prospective, large-scale study to investigate the long-term clinical outcome, decision impact, and medication adherence in HR+ early-stage breast cancer patients receiving BCI testing as part of routine clinical care. Per protocol, physicians and patients completed pre- and post-BCI test questionnaires to assess the following: physician decision-making regarding EET; physician confidence with decision-making; patient preferences for EET; patient concerns about the cost, side effects, drug safety and benefit of EET; and patient satisfaction regarding treatment recommendation. Pre- and post-BCI responses were compared using McNemar’s test and Wilcoxon signed rank test. Results: Pre- and post-BCI test physician and patient questionnaires were completed for 843 and 823 patients, respectively. For the patients included in this analysis, mean age at enrollment was 65y and 88.4% of patients were postmenopausal. 74.7% of tumors were T1, 53.4% were G2, 75.3% N0, and 13.8% HER2-positive. Following BCI testing, physicians changed treatment recommendations for EET in 40.1% (338/843) of patients (p< 0.0001). In cases in which physicians recommended EET prior to BCI testing, 44.7% (214/479) changed their recommendation not to extend endocrine therapy. Of these cases, 98.1% (210/214) were BCI Prognostic low risk and/or BCI (H/I) Predictive low likelihood of benefit from EET. In cases in which physicians did not recommend EET prior to BCI testing, 34.6% (124/358) changed their recommendation in favor of EET. In such cases, 87.1% (108/124) of cases were BCI Prognostic high risk and/or BCI (H/I) Predictive high likelihood of benefit from EET. Further, following BCI testing, 38.8% (327/843) of physicians felt more confident in their recommendation (p< 0.0001). The percentage of physicians having high confidence levels (confident or strongly confident) increased from 58.1% (490/843) before BCI testing to 80.5% (679/843) after BCI testing. The percentage of physicians having low confidence levels (not at all confident, not confident, or ambivalent) decreased from 39.1% (330/843) before BCI testing to 18.7% (158/843) after BCI testing. In addition, 40.5% (341/843) of patients felt more comfortable with their EET decision (p< 0.0001) following BCI testing. Notably, changes in patient preferences for EET correlated with BCI test results. In BCI (H/I)-Low patients, 46.9% (241/514) showed a decreased preference for EET (p< 0.0001) while in BCI (H/I)-High patients, 28.2% (87/309) showed an increased preference for EET (p< 0.0001). Compared with baseline, after BCI testing, significantly more patients were less concerned about cost (20.9%, p< 0.0001), drug safety (25.4%, p=0.0014), and the benefits of EET (29.3%, p=0.0002). No significant change in concern regarding side-effects was observed (p=0.1486). Conclusions: This first analysis in a large patient cohort of the BCI Registry confirms previous findings on the significant clinical decision-making impact of BCI for extending adjuvant endocrine therapy. Incorporating BCI into clinical practice resulted in changes in physician recommendations for EET in over 40% of cases, while at the same time increasing physician confidence in their recommendations. Knowledge of the BCI result also improved patient satisfaction and reduced patient concerns regarding cost, drug safety and benefit of EET. Citation Format: Tara B. Sanft, Jenna Wong, Brandon O’Neal, Natalia Siuliukina, Rachel C. Jankowitz, Mark Pegram, Jenny Fox, Yi Zhang, Kai Treuner, Joyce O’Shaughnessy. Prospective assessment of the decision-making impact of the Breast Cancer Index in the BCI Registry Study [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P2-03-02.

BACKGROUND Giredestrant is a highly potent, nonsteroidal, oral selective estrogen receptor antagonist and degrader (SERD) that was found to be well tolerated and active as a monotherapy and in combination therapy in Phase I/II studies in early BC and pretreated locally advanced/metastatic BC (LA/mBC). Dual HER2 blockade with pertuzumab + trastuzumab (PH) + a taxane (induction therapy) followed by maintenance PH is the first-line standard of care for most patients (pts) with HER2+ LA/mBC. Despite HER2–ER blockade synergy, paucity of Phase III data evaluating maintenance PH + endocrine therapy (ET) vs. PH in pts with ER+/HER2+ LA/mBC leads to variable use of ET in this setting. Adding giredestrant to the maintenance phase could improve outcomes. TRIAL DESIGN This is a Phase III, randomized, two-arm, open-label, multicenter study evaluating the efficacy and safety of giredestrant + the fixed-dose combination of PH for subcutaneous injection (PH FDC SC) vs. PH FDC SC after induction therapy with PH FDC SC + a taxane in pts with ER+/HER2+ LA/mBC. In the induction phase, pts will receive 4–6 PH FDC SC cycles (1200 mg P/600 mg H in the first cycle, followed by 600/600 mg every 3 weeks) + a taxane (investigator choice of docetaxel/paclitaxel). Pts deriving clinical benefit may receive two additional cycles per investigator’s discretion. Pts completing ≥4 induction therapy cycles, achieving at least stable disease, and with a left ventricular ejection fraction (LVEF) ≥50% will be randomly assigned 1:1 to maintenance giredestrant 30 mg/day + PH FDC SC every 3 weeks or PH FDC SC only, until disease progression (PD). ET (aromatase inhibitor/tamoxifen) will be allowed in the PH FDC SC-only arm. Study treatment will continue until PD, limiting toxicity, death, or consent withdrawal. ELIGIBILITY Enrolled pts must have ER+/HER2+ LA/mBC, disease-free interval from completion of (neo)adjuvant non-ET ≥6 months, Eastern Cooperative Oncology Group performance status 0/1, LVEF ≥50%, and adequate organ function. Pts with prior SERD treatment or presence of symptomatic central nervous system metastases will be excluded. All men and pre-/perimenopausal women must be eligible for a luteinizing hormone-releasing hormone agonist. AIMS The primary endpoint is investigator-assessed, maintenance progression-free survival. Secondary endpoints include overall survival (OS), objective response rate, duration of response, clinical benefit rate, pt-reported outcomes, and safety. STATISTICAL METHODS The primary endpoint analysis will use a stratified log-rank test at an overall 0.05 significance level (two-sided). An interim OS analysis is planned, and an independent data monitoring committee will be in place. ACCRUAL The study is open for enrollment. Approximately 812 pts will be enrolled in the induction phase, to allow for approximately 730 pts to be randomized in the maintenance phase. CONTACT INFORMATION For more information or to refer a patient, email global.rochegenentechtrials@roche.com or call 1-888-662-6728 (USA only). Clinicaltrials.gov number: NCT05296798. Citation Format: Sherko Küemmel, Catherine Harper-Wynne, Yeon H. Park, Fábio Franke, Michelino De Laurentiis, Eva Schumacher-Wulf, Daniel Eiger, Sarah Heeson, Mahesh Shivhare, Eleonora Restuccia, Joyce O’Shaughnessy. heredERA Breast Cancer: Phase III study of first-line, fixed-dose combination of pertuzumab and trastuzumab for subcutaneous injection ± giredestrant (GDC-9545) for estrogen receptor+, HER2+ advanced breast cancer [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr OT2-03-01.

Triple-negative breast cancer (TNBC) is an aggressive malignancy for which cytotoxic chemotherapy remains the backbone of treatment. Trilaciclib is an intravenous cyclin-dependent kinase 4/6 inhibitor that induces transient cell cycle arrest of hematopoietic stem and progenitor cells and immune cells during chemotherapy exposure, protecting them from chemotherapy-induced damage and enhancing immune activity. Administration of trilaciclib prior to gemcitabine plus carboplatin (GCb) significantly improved overall survival (OS) compared with GCb alone in an open-label phase II trial in patients with metastatic TNBC, potentially through protection and direct activation of immune function. The randomized, double-blind, placebo-controlled, phase III PRESERVE 2 trial will evaluate the efficacy and safety of trilaciclib administered prior to GCb in patients with locally advanced unresectable or metastatic TNBC. Clinical Trial Registration: NCT04799249 ( ClinicalTrials.gov )

Background The multinational BREAKOUT study (NCT03078036) sought to determine the prevalence of germline BRCA1/2 (gBRCA1/2) and somatic BRCA1/2 (sBRCA1/2) mutations and mutations in other homologous recombination repair (HRR) genes in women with HER2-negative metastatic breast cancer (MBC) starting first-line chemotherapy. Methods Genetic testing for gBRCA, sBRCA, and HRR gene mutations was performed in patients who started first-line chemotherapy for MBC in the last 90 days (341 patients across 14 countries) who were not selected based on risk factors for gBRCA mutations. We report data from the Asian cohort, which included patients in Japan (7 sites), South Korea (10 sites), and Taiwan (8 sites). Results Of 116 patients screened, 104 patients were enrolled in the Asian cohort. The median age was 53.0 (range 25–87) years. gBRCA1/2, gBRCA1, and gBRCA2 mutations were detected in 10.6% (11/104), 5.8% (6/104), and 4.8% (5/104) of patients, respectively; none had mutations in both gBRCA1 and gBRCA2. gBRCA1/2 mutations were detected in 10.0% (6/60) and 11.6% (5/43) of patients with hormone receptor-positive and triple-negative MBC, respectively. HRR gene mutations were tested in 48 patients without gBRCA mutations, and 5 (10.4%) had at least one HRR mutation in sBRCA, ATM, PALB2, and CHEK2. Conclusion We report for the first time the prevalence of gBRCA and HRR mutations in an Asian cohort of patients with HER2-negative MBC. Our results suggest that BRCA mutation testing is valuable to determine appropriate treatment options for patients with hormone receptor-positive or triple-negative MBC. Study registration NCT03078036.

Objective/Background We performed a retrospective analysis of longitudinal real-world data (RWD) from patients with breast cancer to replicate results from clinical studies and demonstrate the feasibility of generating real-world evidence. We also assessed the value of transcriptome profiling as a complementary tool for determining molecular subtypes. Methods De-identified, longitudinal data were analyzed after abstraction from records of patients with breast cancer in the United States (US) structured and stored in the Tempus database. Demographics, clinical characteristics, molecular subtype, treatment history, and survival outcomes were assessed according to strict qualitative criteria. RNA sequencing and clinical data were used to predict molecular subtypes and signaling pathway enrichment. Results The clinical abstraction cohort (n = 4000) mirrored the demographics and clinical characteristics of patients with breast cancer in the US, indicating feasibility for RWE generation. Among patients who were human epidermal growth factor receptor 2-positive (HER2+), 74.2% received anti-HER2 therapy, with ∼70% starting within 3 months of a positive test result. Most non-treated patients were early stage. In this RWD set, 31.7% of patients with HER2+ immunohistochemistry (IHC) had discordant fluorescence in situ hybridization results recorded. Among patients with multiple HER2 IHC results at diagnosis, 18.6% exhibited intra-test discordance. Through development of a whole-transcriptome model to predict IHC receptor status in the molecular sequenced cohort (n = 400), molecular subtypes were resolved for all patients (n = 36) with equivocal HER2 statuses from abstracted test results. Receptor-related signaling pathways were differentially enriched between clinical molecular subtypes. Conclusions RWD in the Tempus database mirrors the overall population of patients with breast cancer in the US. These results suggest that real-time, RWD analyses are feasible in a large, highly heterogeneous database. Furthermore, molecular data may aid deficiencies and discrepancies observed from breast cancer RWD.

We investigated first-line (1L) treatment patterns and predictors of taxane use to better understand the evolving metastatic triple-negative breast cancer (mTNBC) treatment landscape. This retrospective analysis of the Truven Health MarketScan® (Somers, NY, USA) Database included women with mTNBC who received 1L therapy within six months of diagnosis (January 2005–June 2015). Multivariate logistic regression models identified predictors of taxane use, adjusting for prognostic factors. A total of 2271 women with newly diagnosed mTNBC received 1L treatment during the study period. Half received a 1L taxane (53%), more often in combination than as monotherapy (58% versus 42%), though this varied by specific taxane. Nab-Paclitaxel monotherapy increased substantially after 2010. More recent treatment year (odds ratio, 2.16 (95% CI 1.69–2.76]) and number of metastases (≥3 versus 1: 1.73 (1.25–2.40)) predicted taxane monotherapy versus combination. Having a health maintenance organization versus a preferred provider organization plan predicted less nab-paclitaxel versus paclitaxel (0.32 (0.13–0.80)) or docetaxel (0.30 (0.10–0.89)) use. More recent index year (2011–2015 vs. 2005–2010) was the only predictor favoring nab-paclitaxel versus paclitaxel (2.01 (1.26–3.21)) or docetaxel (3.63 (2.11–6.26)). Taxane-containing regimens remained the most common 1L mTNBC treatments. Paclitaxel and nab-paclitaxel use changed substantially over time, with nab-paclitaxel use associated with insurance coverage.

In MONARCH 3, continuous dosing of abemaciclib with an aromatase inhibitor (AI) conferred significant clinical benefit to postmenopausal women with HR+, HER2− advanced breast cancer. We report data for clinically prognostic subgroups: liver metastases, progesterone receptor status, tumor grade, bone-only disease, ECOG performance status, and treatment-free interval (TFI) from an additional 12-month follow-up (after final progression-free survival [PFS] readout). In the intent-to-treat population, after median follow-up of approximately 39 months, the updated PFS was 28.2 versus 14.8 months (hazard ratio [HR], 0.525; 95% confidence interval, 0.415–0.665) in abemaciclib versus placebo arms, respectively. Time to chemotherapy (HR, 0.513), time to second disease progression (HR, 0.637), and duration of response (HR, 0.466) were also statistically significantly prolonged with the addition of abemaciclib to AI. Treatment benefit was observed across all subgroups, as evidenced by objective response rate change from the addition of abemaciclib to AI, with the largest effects observed in patients with liver metastases, progesterone receptor-negative tumors, high-grade tumors, or TFI

Breast cancer; Drug safety Càncer de mama; Seguretat dels medicaments Cáncer de mama; Seguridad de los medicamentos Sacituzumab govitecan (SG) is an anti-Trop-2 antibody-drug conjugate with an SN-38 payload. In the ASCENT study, patients with metastatic triple-negative breast cancer (mTNBC) relapsed/refractory to ≥2 prior chemotherapy regimens (≥1 in the metastatic setting), received SG or single-agent treatment of physician’s choice (eribulin, vinorelbine, capecitabine, or gemcitabine). This ASCENT safety analysis includes the impact of age and UGT1A1 polymorphisms, which hinder SN-38 detoxification. SG demonstrated a manageable safety profile in patients with mTNBC, including those ≥65 years; neutropenia/diarrhea are key adverse events (AE). Patients with UGT1A1 *28/*28 genotype versus those with 1/*28 and *1/*1 genotypes had higher rates of grade ≥3 SG-related neutropenia (59% vs 47% and 53%), febrile neutropenia (18% vs 5% and 3%), anemia (15% vs 6% and 4%), and diarrhea (15% vs 9% and 10%), respectively. Individuals with UGT1A1 *28/*28 genotype should be monitored closely; active monitoring and routine AE management allow optimal therapeutic exposure of SG. This study was sponsored by Immunomedics, Inc., a subsidiary of Gilead Sciences, Inc. We thank the ASCENT patients, their caregivers, study investigators, and team members. We thank William A. Wegener, MD, PhD, Robert M. Sharkey, PhD, and Pius Maliakal, PhD, former employees of Immunomedics, for their contributions to the development of the ASCENT protocol and the clinical development of sacituzumab govitecan. Medical writing and editorial assistance were provided by Robert Rydzewski, MS, CMPP, and Shala Thomas, PhD, CMPP, of Team 9 Science, and funded by Immunomedics, Inc., a subsidiary of Gilead Sciences, Inc.

Quality of life; Sacituzumab govitecan; Triple-negative breast neoplasms Qualitat de vida; Sacituzumab govitecan; Neoplàsies de mama triple negatiu Calidad de vida; Sacituzumab govitecan; Neoplasias de mama triple negativo Background The antibody–drug conjugate sacituzumab govitecan (SG) prolongs progression-free survival and overall survival in patients with refractory/relapsed metastatic triple-negative breast cancer (mTNBC). Here, we investigated its effect on health-related quality of life (HRQoL). Methods This analysis was based on the open-label phase III ASCENT trial (NCT02574455). Adults with refractory/relapsed mTNBC who had received ≥2 prior systemic therapies (≥1 in the metastatic setting) were randomised 1:1 to SG or treatment of physician's choice (TPC; capecitabine, eribulin, vinorelbine, or gemcitabine). HRQoL was assessed on day 1 of each treatment cycle using the EORTC QLQ-C30. Score changes from baseline were analysed using linear mixed-effect models for repeated measures. Stratified Cox regressions evaluated time to first clinically meaningful change of HRQoL. Results The analysis population comprised 236 patients randomised to SG and 183 to TPC. For global health status (GHS)/QoL, physical functioning, fatigue, and pain, changes from baseline were superior for SG versus TPC. Compared with TPC, SG was inferior regarding changes from baseline for nausea/vomiting and diarrhoea but non-inferior for other QLQ-C30 domains. Median time to first clinically meaningful worsening was longer for SG than for TPC for physical functioning (22.1 versus 12.1 weeks, P < 0.001), role functioning (11.4 versus 7.1 weeks, P < 0.001), fatigue (7.7 versus 6.0 weeks, P < 0.05), and pain (21.6 versus 9.9 weeks, P < 0.001). Conclusions SG was generally associated with greater improvements and delayed worsening of HRQoL scores compared with TPC. This supports the favourable profile of SG as an mTNBC treatment. This work was sponsored by Gilead Sciences.

To characterise risk of anaphylaxis/hypersensitivity with intravenous pertuzumab plus trastuzumab (PH IV), the fixed-dose combination of pertuzumab and trastuzumab for subcutaneous injection (PH FDC SC) or concomitant chemotherapy to support potential administration of PH FDC SC by healthcare professionals outside clinics.A cumulative search for anaphylaxis/hypersensitivity (Roche Standard Adverse Event Group Terms) was performed for all pivotal trials cited in the current EMA P IV/PH FDC SC summaries of product characteristics: MBC: NCT00567190, NCT02402712; EBC: NCT01358877, NCT00545688, NCT00976989, NCT02132949, NCT03493854 and NCT03674112. Occurrence, incidence and severity of events were analysed and a time-trend analysis (by cycle) was performed.This analysis includes 4772 patients who received PH IV and/or PH FDC SC. Incidence of all-grade (grade ≥3) anaphylaxis/hypersensitivity events: 3-11% (≤2%) for PH IV MBC trials; 1-13% (0-3%) for PH IV EBC trials; and 2-3% (1%; not related to PH FDC SC) for PH FDC SC EBC trials. Discontinuations due to anaphylaxis/hypersensitivity were rare for PH IV (generally1% except two arms of TRYPHAENA: 1% and 3%); no discontinuations of PH FDC SC have been recorded so far. Time-trend analysis showed that most events were reported during the first 6-8 cycles with concurrent chemotherapy, with a decrease in later cycles (except MetaPHER).PH IV and PH FDC SC were well tolerated, with few grade ≥3 anaphylaxis/hypersensitivity events reported with PH IV and no grade ≥3 related events with PH FDC SC. Most events occurred during chemotherapy.

Objective: This study evaluated the cost–effectiveness of pembrolizumab/chemotherapy combinations for previously untreated metastatic triple-negative breast cancer patients in the USA with PD-L1 combined positive score ≥10. Methods: A partitioned-survival model was developed to project health outcomes and direct medical costs over a 20-year time horizon. Efficacy and safety data were from randomized clinical trials. Comparative effectiveness of indirect comparators was assessed using network meta-analyses. A series of sensitivity analyses were performed to test the robustness of the results. Results: Pembrolizumab/chemotherapy resulted in total quality-adjusted life-year (QALY) gains of 0.70 years and incremental cost–effectiveness ratio of US$182,732/QALY compared with chemotherapy alone. The incremental cost–effectiveness ratio for pembrolizumab/nab-paclitaxel versus atezolizumab/nab-paclitaxel was US$44,157/QALY. Sensitivity analyses showed the results were robust over plausible values of model inputs. Conclusion: Pembrolizumab/chemotherapy is cost effective compared with chemotherapy as well as atezolizumab/nab-paclitaxel as first-line treatment for PD-L1-positive metastatic triple-negative breast cancer from a US payer perspective.

Systemic Therapies for HER2-Positive Metastatic Breast Cancer Study (SystHERs, NCT01615068) was a prospective, observational disease registry designed to identify treatment patterns and clinical outcomes in patients with HER2-positive metastatic breast cancer (MBC) in real-world treatment settings. SystHERs enrolled patients aged ≥ 18 years with recently diagnosed HER2-positive MBC. Treatment regimens and clinical management were determined by the treating physician. In this analysis, patients were compared descriptively by first-line treatment, age, or race. Multivariate logistic regression was used to examine the associations between baseline variables and treatment selections. Clinical outcomes were assessed in patients treated with trastuzumab (Herceptin [H]) + pertuzumab (Perjeta [P]). Patients were enrolled from June 2012 to June 2016. As of February 22, 2018, 948 patients from 135 US treatment sites had received first-line treatment, including HP (n = 711), H without P (n = 175), or no H (n = 62) (with or without chemotherapy and/or hormonal therapy). Overall, 68.7% received HP + taxane and 9.3% received H without P + taxane. Patients aged

Background: Trophoblast cell-surface antigen-2 (Trop-2) is highly expressed in many epithelial tumors, including triple-negative breast cancer (TNBC). Sacituzumab govitecan (SG) is an antibody-drug conjugate composed of an anti-Trop-2 antibody coupled to SN-38, an active metabolite of irinotecan, via a unique hydrolyzable linker that allows for SN-38 release intracellularly and in the tumor microenvironment (bystander effect). Preclinical studies have shown a great range of efficacy with SG in mice bearing tumors with low, moderate, and high Trop-2 expression levels. We report subgroup analyses by Trop-2 expression from ASCENT, a randomized, phase 3 confirmatory study of SG versus standard-of-care chemotherapy in patients with metastatic TNBC (mTNBC). Methods: In the global, multicenter, open-label, phase 3 ASCENT study (NCT02574455), 529 patients with mTNBC refractory to or relapsing after at least 2 prior chemotherapies were randomized 1:1 to receive SG (10 mg/kg intravenously on days 1 and 8 every 21 days) or single-agent treatment of physician’s choice (capecitabine, eribulin, vinorelbine, or gemcitabine) until disease progression or unacceptable toxicity. The primary endpoint was progression-free survival (PFS) measured by central independent review per RECIST v1.1. Secondary endpoints included objective response rate (ORR) per RECIST v1.1, duration of response, overall survival (OS), and safety. Exploratory endpoints included biomarker assessments, including Trop-2 and BRCA1/2. Trop-2 expression was assessed using a validated immunohistochemistry assay. Results: Subgroup analyses by biomarker expression including Trop-2 and BRCA1/2 were performed, and outcomes by PFS, OS, ORR, and safety results will be reported. Conclusions: These analyses will provide further insights into the relationship of Trop-2 expression and the activity of SG in previously treated patients with mTNBC. Citation Format: Sara A. Hurvitz, Sara M. Tolaney, Kevin Punie, Delphine Loirat, Mafalda Oliveira, Kevin Kalinsky, Amelia Zelnak, Philippe Aftimos, Florence Dalenc, Sagar Sardesai, Erika Hamiltion, Priyanka Sharma, Sabela Recalde, Eva Ciruelos Gil, Tiffany Traina, Joyce O'Shaughnessy, Javier Cortés, Michaela Tsai, Linda Vahdat, Véronique Diéras, Lisa Carey, Hope S. Rugo, David M. Goldenberg, Quan Hong, Martin Olivo, Loretta M. Itri, Aditya Bardia. Biomarker evaluation in the phase 3 ASCENT study of sacituzumab govitecan versus chemotherapy in patients with metastatic triple-negative breast cancer [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr GS3-06.

Background: CDK4/6 inhibitors have emerged as the standard of care for HR+ MBC. However, there is limited insight into the potential benefit of abemaciclib following prior progression on palbociclib or ribociclib. Based on a multi-center cohort of patients with HR+ MBC who had received abemaciclib after prior palbociclib progression (Wander SA et al ASCO 2019), we have previously reported that abemaciclib after prior CDK4/6i progression was well tolerated and that a subset of patients derived durable clinical benefit. Identifying molecular predictors of sensitivity to abemaciclib after prior CDK4/6i progression constitutes an important area of research. Given the high frequency of ESR1 mutations in HR+ MBC with antiestrogen resistance, we evaluated the translational impact of ESR1 mutations in mediating response to abemaciclib in this setting. Methods: To evaluate abemaciclib sensitivity in ESR1 mutant cell lines, T47D HR+ breast cancer cells were modified to over-express multiple mutant ESR1 isoforms via lentiviral infection and antibiotic selection. These isoforms included ESR1 Y537S, Y537N, and D538G. In an additional T47D cell line, RB1 expression was knocked down via CRISPR. The resulting derivative cell lines were grown in the absence of estrogen (via charcoal-stripped serum, CSS) or in escalating doses of abemaciclib. Cell viability was measured via cell-titer-glo assay. For clinical validation, we identified patients with MBC who had ESR1 mutations detected by targeted sequencing of cell-free DNA (cfDNA), via CLIA certified Guardant assay, and had abemaciclib exposure following prior progression on palbociclib or ribociclib in the existing multi-center cohort from six US institutions. Results: All ESR1 mutant derivative cells demonstrated enhanced growth in estrogen deprivation compared to GFP controls, as expected, and were similarly sensitive to escalating doses of abemaciclib monotherapy in vitro, suggesting that ESR1 mutations do not confer resistance to abemaciclib. Interestingly, two patients with ESR1 mutations (in the absence of concurrent driver alterations in RB1, FGFR, CCNE2, and ERBB2) demonstrated progression on palbociclib and sensitivity to abemaciclib. In one patient, cfDNA obtained prior to palbociclib and fulvestrant exposure failed to reveal any ESR1 alteration. Following progression on palbociclib, and prior to sequential exposure to abemaciclib, an ESR1 Y537N alteration was identified. The patient went on to receive 16 months of abemaciclib monotherapy. In a second patient, an ESR1 D538G alteration was identified following progression on palbociclib and fulvestrant. The patient had several intervening regimens, and subsequently went on to receive abemaciclib and fulvestrant for 16 months. RB1-null T47D cells were resistant to abemaciclib monotherapy in vitro, as expected and, in the clinical dataset, the presence of alterations in previously identified genomic mediators of CDK4/6i resistance, such as RB1, were associated with progression on both palbociclib and abemaciclib. Conclusions: HR+ breast cancer cells expressing mutant ESR1 isoforms were resistant to estrogen deprivation but retained sensitivity to abemaciclib in vitro. Furthermore, patients harboring ESR1 mutations via targeted sequencing of cfDNA, in the absence of other known mediators of CDK4/6i resistance, were shown to derive clinical benefit from abemaciclib following prior progression on palbociclib. These results suggest that patients with HR+ MBC, ESR1 mutation, and clinical resistance to anti-estrogen treatment and palbociclib may be candidates for abemaciclib treatment. Further research is warranted to confirm these novel translational observations. Citation Format: Seth A. Wander, Hyo S. Han, Gabriela N. Johnson, Maxwell R. Lloyd, Pingping Mao, Utthara Nayar, Kailey Kowalski, Casey R. Stein, Veronica Mariotti, Leslie SL Kim, Maren Levin, Jing Xi, Apurva Pandey, Siobhan Dunne, Azadeh Nasrazadani, Adam Brufsky, Kevin Kalinsky, Cynthia X Ma, Joyce O’Shaughnessy, Nikhil Wagle, Aditya Bardia. Esr1 mutation as a potential predictor of abemaciclib benefit following prior cdk4/6 inhibitor (cdk4/6i) progression in hormone receptor-positive (hr+) metastatic breast cancer (mbc): A translational investigation [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS5-10.

Background: Trophoblast cell-surface antigen-2 (Trop-2) is highly expressed in many epithelial tumors, including triple-negative breast cancer (TNBC). Sacituzumab govitecan (SG) is an antibody-drug conjugate composed of an anti-Trop-2 antibody coupled to SN-38, the active metabolite of irinotecan, via a unique hydrolyzable linker that allows SN-38 release intracellularly and in the tumor microenvironment (bystander effect). SG received accelerated approval in April 2020 for the treatment of patients with metastatic TNBC (mTNBC) who received at least 2 prior therapies for metastatic disease. The most common adverse events (AEs) observed with SG are neutropenia and gastrointestinal toxicity, also seen with irinotecan. To provide further information on SG, additional safety analyses from ASCENT, a randomized, phase 3 confirmatory study of SG versus standard-of-care chemotherapy in patients with mTNBC, will be reported. Methods: In the global, multicenter, open-label, phase 3 ASCENT study (NCT02574455), 529 patients with mTNBC refractory to or relapsing after at least 2 prior chemotherapies were randomized 1:1 to receive SG (10 mg/kg intravenously on days 1 and 8 every 21 days) or single-agent treatment of physician’s choice (capecitabine, eribulin, vinorelbine, or gemcitabine) until disease progression or unacceptable toxicity. The primary endpoint was progression-free survival measured by central independent review per RECIST v1.1. Secondary endpoints included objective response rate, duration of response, overall survival, and safety. An exploratory analysis of incidence of grade 3-5 AEs by UGT1A1 genotype was also performed. Post-hoc analysis of the time to onset and duration of key AEs will be performed, and descriptive analyses on alopecia, nausea and vomiting will also be provided. Results: Exploratory safety analyses by UGT1A1 allele status will be shown as well as time to onset and duration of neutropenia and diarrhea. Further descriptive analyses on alopecia, nausea, and vomiting will be provided along with AE management strategies. Conclusions: These analyses will provide further insights into the safety profile of SG and appropriate AE management strategies for patients with previously treated mTNBC to allow optimal therapeutic exposure. Citation Format: Hope S. Rugo, Sara M. Tolaney, Delphine Loirat, Kevin Punie, Aditya Bardia, Sara A. Hurvitz, Joyce O'Shaughnessy, Javier Cortés, Véronique Diéras, Lisa Carey, Luca Gianni, Martine J. Piccart, Sibylle Loibl, David M. Goldenberg, Quan Hong, Martin Olivo, Loretta M. Itri, Kevin Kalinsky. Impact of UGT1A1 status on the safety profile of sacituzumab govitecan in the phase 3 ASCENT study in patients with metastatic triple-negative breast cancer [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS11-09.

BACKGROUND: A subset of TNBCs have homologous recombination deficiency with upregulation of compensatory DNA repair pathways. The combination of TAK-228 and TAK-117 (PIKTOR), investigational oral TORC1/2 and PI3Kα selective inhibitors, respectively, is hypothesized to increase genomic instability (GI) and to increase DDRD, leading to increased sensitivity to DNA damaging chemotherapy and to checkpoint inhibitors in metTNBC pts. METHODS: 10 metTNBC pts received 4 mg PO TAK-228 and 200 mg PO TAK-117 QDx3d QW until disease progression (PD), followed by cis 75 mg/m2 plus nab pac 220 mg/m2 for up to 6 cycles. Primary endpoints were objective response rate with cis/nab pac and safety. Blood samples and biopsies of metastatic lesions were collected prior to and at PD on PIKTOR. Blood CTC analyses included enumeration, cell morphology, phenotypic heterogeneity, and predicted genomic instability (pGI) derived from cell phenotypes. RESULTS: 10 pts received PIKTOR followed by cis/nab pac. Median age: 51 yrs; median number of prior chemotherapy regimens was 3 (range, 1-5); 7 pts had prior carboplatin; sites of metastases: lymph nodes (n=8); lung (n=6); chest wall (n=1); bone (n=1); brain (n=1). Median time on PIKTOR was 8 wks (range, 3-14). With cis/nab pac, 1 pt had PR, 2 had SD > 6 mos, 1 had SD and 6 had PD. 2 SD pts (sites LNs and bone) and 1 PD pt (sites LNs), all carboplatin-pretreated, whose pre-PIKTOR BCs were PDL1-negative (2 pts) or unknown (1 pt) have durable SD on pembrolizumab post-cis/nab pac for 1+ yrs. PIKTOR related AEs ≥30% included: fatigue (90%); nausea (80%); diarrhea (60%); vomiting (40%); stomatitis (40%); hyperglycemia (30%); rash (30%); cough (30%); chest pain (30%). Incidence and grade of cis/nab pac-related AEs were not greater than expected with this regimen. At PD on PIKTOR, higher CTC burden and pGI+ CTCs were observed in a subset of pts suggesting that some CTCs may have developed greater GI with PIKTOR treatment. Next generation sequencing (NGS) and reverse phase protein array (RPPA) analyses of biomarkers of DNA repair pathways pre-and post-PIKTOR tissues are underway and will be presented at the meeting. CONCLUSIONS: Priming pts’ metTNBC with PIKTOR did not lead to durable responses with cis/nab pac in most pts in this pretreated population. However, 3/10 pts who had carboplatin-pretreated disease in LNs +/- bone, have highly durable SD on pembrolizumab following PIKTOR therapy. Citation Format: Joyce O'Shaughnessy, Esther San Roman Rodriguez, Priscilla Ontiveros, Rick Wenstrup, Tiziano Pramparo, Jessica Lang, Victoria Zismann, Natalia Briones, William Hendricks, Virginia Espina, Claudius Mueller, Maren K Levin. Pilot trial of priming with oral TAK-228 and TAK-117 (PIKTOR) to increase DNA damage repair deficiency (DDRD) followed by cisplatin (cis) and nab paclitaxel (nab pac) in chemotherapy-pretreated metastatic triple negative breast cancer (metTNBC) pts [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS11-25.