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Background: Prior, retrospective analysis of nightly fasting among women with breast cancer suggests that fasting less than 13 hours per night may be associated with higher risk of breast cancer recurrence. Small studies suggest that fasting duration can influence inflammation, obesity, sleep, and other potential mediators of breast cancer recurrence risk. Prolonged overnight fasting is a simple, nonpharmacological behavioral intervention strategy that may be doable for most patients. We designed this pilot study to prospectively evaluate the feasibility of prolonged overnight fasting among breast cancer survivors. Methods: We designed a single-arm, pilot study to evaluate the feasibility of fasting for 13 hours overnight for a 12-week period among women with a history of early stage breast cancer (I to III) who had completed initial cancer therapy at least 6 months prior. Baseline and end of study assessments included measurements of body mass index (BMI), quality of life (QOL) (Functional Assessment of Cancer Therapy - General (FACT-G)), mood (Hospital Anxiety and Depression Scale (HADS)), fatigue (Functional Assessment of Chronic Illness Therapy (FACIT) - Fatigue), levels of physical activity (Godin Leisure-Time Exercise Questionnaire), and blood biomarkers (expanded lipid profile, hemoglobin A1c, C-reactive protein, interleukin-6, tumor necrosis factor alpha, leptin, adiponectin). Patient-reported outcome (PRO) surveys were also administered at 6 weeks. Feasibility was defined as ≥ 60% of participants documenting fasting in the food diary for 13 hours on at least 70% of nights during the study period. Changes in study measures from baseline were evaluated using Wilcoxon signed-rank tests. Results: Between July 2020 and January 2021, we enrolled 40 women with a history of breast cancer. Participants had a median age of 59.9 (range 34.9-76.3) and median time since diagnosis was 4.5 years (range 0.8-20.7). At baseline, BMI was normal (18.5-24.9) in 40.0%, overweight (25-29.9) in 37.5%, and obese (≥30) in 22.5%. Forty-two and a half percent had Stage I cancer, 42.5% stage II, and 15.0% stage III. Sixty-five percent were on hormonal therapy. Ninety-five percent of participants fasted ≥ 13 hours for at least 70% of study days (95% CI 83%-99%). At 6 weeks, there was a statistically significant improvement in anxiety (p=.0007). No other significant changes were seen in PROs. At 12 weeks, there were statistically significant improvements in BMI (p=.0072), anxiety (p=.0141), depression (p=.0048), and fatigue (p=.0105). There was no association between change in BMI during the study and baseline BMI category, age, or endocrine therapy. There was no significant change in overall QOL, physical activity levels, or blood biomarkers at 12 weeks. Conclusions: Prolonged overnight fasting is feasible in the breast cancer population and may improve BMI, mood, and fatigue without a detrimental effect on overall QOL. The data from this study support the need for a larger, longer randomized study of prolonged overnight fasting in the breast cancer population to further evaluate the effects on body composition, mood, QOL, metabolic markers, and risk of recurrence. Table 1.Impact of Prolonged Overnight Fasting among Breast Cancer SurvivorsStudy AssessmentMedian at baselineMedian at 12 weeksMedian within-participant changep-valueBody Mass Index (kg/m2)26.4225.80-0.380.0072HADS - Depression1.001.00-1.000.0048HADS - Anxiety4.504.00-0.500.0141FACIT - Fatigue47.5049.821.000.0105FACT-G - Quality of Life95.2096.840.910.4933Physical Activity Level40.5039.000.000.3340Hemoglobin A1c (mg/dL)5.455.400.000.2758High-density lipoprotein (mg/dL)72.0073.00-2.000.4688Low-density lipoprotein (mg/dL)92.0099.001.000.5626Total Cholesterol (mg/dL)193.00192.003.000.6569C-reactive protein (mg/L)1.500.90-0.100.1043Interleukin-6 (pg/mL)2.001.90-0.300.1213Tumor Necrosis Factor α (pg/mL)0.740.74-0.050.2898Adiponectin (ug/mL)12.0012.000.000.0682Leptin (ng/mL)7.158.30-0.100.8418 Citation Format: Elizabeth K. O'Donnell, Yael N. Shapiro, Amy Comander, Steven J. Isakoff, Beverly Moy, Laura Spring, Seth Wander, Irene Kuter, Jennifer Shin, Jerry Younger, Michelle Specht, Chryssanthi Kourniotis, Carol Sullivan, Loren Winters, Nora Horick, Jeffrey Peppercorn. Pilot study to assess prolonged nightly fasting in breast cancer survivors (LONGFAST) [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 PD5-11.

Background: Survival advantages with neoadjuvant chemotherapy (NACT) have been observed in patients (pts) with locally advanced breast cancer (BC) who achieve pathological complete response (pCR). Predicting risk of early recurrence in pts without pCR remains difficult. Circulating tumor DNA (ctDNA) may be a biomarker of neoadjuvant therapy response and recurrence. This study applied tumor genotyping of peripheral blood in pts with HER2− tumor BRCA-mutated (tBRCAm) BC treated with neoadjuvant niraparib. The relationship between ctDNA and tumor response was also characterized, with a focus on circulating TP53 mutant allelic frequency (MAF). Methods: Blood was collected from 21 pts enrolled in the study (NCT03329937) evaluating neoadjuvant niraparib in pts with localized HER2− tBRCAm BC. Pts received niraparib 200 mg once daily for two 28-day cycles. After 2 cycles, pts underwent surgery or received up to 6 cycles of niraparib and/or NACT prior to surgery. Blood samples were collected at screening, Cycle 1 Day 28 (C1D28), Cycle 2 Day 28 (C2D28), and pre-surgery. Ultrasound (USG) was done after each cycle and MRI after Cycle 2. Next-generation sequencing of cell-free plasma DNA was carried out using a proprietary target capture and analysis (Paweletz, Clin Cancer Res 2016). Results: ctDNA and TP53 mutations (TP53m) were detected at screening in 10/21 pts (47.6%). Across all 21 pts there was a correlation between TP53 MAF and baseline tumor stage (T) (mean [standard deviation], T1 0 [0], T2 0.05 [0.09], and T3 0.21 [0.12]; P=0.005). Linear regression modelling showed a positive correlation between tumor volume and baseline TP53 MAF (R2=0.206, P=0.0386). Baseline TP53 MAF also appeared to be associated with advanced disease stage (Table 1). Depletion of detectable TP53m from baseline was evident by C1D28 and persisted to pre-surgery (Table 2). This corresponded with decreases in tumor volume at C1D28 and further decreases at C2D28. Of 11 pts analyzed, 6 pts with >90% tumor volume decreases by MRI or USG at C2D28 had sustained TP53m depletion. Three pts had pCR; of these, 2 had sustained TP53m depletion (data unavailable for third pCR pt). Two pts with less robust tumor responses had increased pre-surgery TP53 MAF. Conclusions: We report the potential utility of ctDNA as a predictive biomarker for neoadjuvant niraparib response in pts with HER2− tBRCAm BC. Although sample size limited analysis of genes other than TP53, baseline ctDNA strongly correlated with tumor volume, and TP53 MAF was associated with tumor volume and trended towards association with disease stage. Longitudinal analysis of TP53 MAF suggested a correlation with niraparib response. Further study of ctDNA dynamics during NACT and correlation with pCR and long-term clinical outcomes is warranted. Funding: GlaxoSmithKline (GSK) study 213355; NCT03329937. Medical writing support was provided by Fishawack Indicia, part of Fishawack Health, funded by GSK. Table 1.Baseline TP53 MAF association with disease stage and subtypeTP53 MAFDisease Stage (I–III)Disease SubtypeStage IStage IIStage IIIHR+TNBC(n=8)(n=10)(n=3)(n=6)(n=15)Mean (SD)0.01 (0.02)0.07 (0.12)0.10 (0.05)0.02 (0.02)0.06 (0.10)HR, hormone receptor; MAF, mutant allelic frequency; SD, standard deviation; TNBC, triple-negative breast cancer. Table 2.TP53 MAF correlation with tumor volume decrease by ultrasound and MRIOutcomeScreeningCycle 1 Day 28 Cycle 2 Day 28 Pre-Surgeryn11997TP53 MAF, mean, (SD)0.09 (0.11)000.01 (0.02)n11112Percent change in tumor volume from baseline by MRI, mean (SD)-N/A*−72.6 (22.5)N/A*Percent change in tumor volume from baseline by ultrasound, mean (SD)-−60.8 (24.0)−80.6 (21.8)−95.9 (4.3)*MRI was only performed at Cycle 2 Day 28. MAF, mutant allelic frequency; MRI, magnetic resonance imaging; N/A, not applicable; SD, standard deviation. Citation Format: Ming Shan, Laura Spring, Minetta C Liu, Erika Hamilton, Hanna Irie, Cesar A Santa-Maria, Steven J Isakoff, James Reeves, Leif W Ellisen, Lee P Lim, Kavita Garg, Caterina Bertucci, Bin Feng, Hailei Zhang, Kaiming Sun, Julie R Graham, Erin Hofstatter, Hyo Han. Relationship between circulating tumor DNA and response to neoadjuvant niraparib in HER2-negative, BRCA-mutated 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 P5-13-21.

Background: Patients’ understanding of their breast cancer (BC) diagnosis is important in improving treatment adherence, shared decision-making, and clinical trial matching. However, studies have reported discrepancies between electronic medical record (EMR) and patient reported information. Using data collected from a pilot study of the Outcomes4Me patient empowerment and clinical trial matching App, we analyzed concordance of patient reported disease characteristics compared to EMR data. Methods: Data was analyzed from a single institution pilot study (NCT04262518) evaluating the feasibility of introducing the Outcomes4Me app into routine BC care. Eligibility included BC patients with any subtype or stage of invasive cancer presenting with a new diagnosis or for follow-up on active therapy. We compared patient reported characteristics within a study specific survey and/or the Outcomes4Me app for stage (metastatic or not metastatic), recurrence history, hormone receptor status, HER2, and surgery history with the data recorded in the EMR. All statistics were descriptive. We conducted the same comparison between patient reported clinical characteristics among real world users of the Outcome4Me app and EMR records downloaded by that cohort of patients. Results: Between June 2020 and December 2020, 107 patients were enrolled. Baseline demographics: 90% White, 4% Black, 3% Asian; 37% with a college degree, and 43% with post college education; 66% hormone positive/HER2-, 20% HER2+, and 13% triple negative BC; 31% were stage 4. Concordance between the survey or App questionnaire and the EMR is shown in the Table. Comparing EMR and survey data, 62% of patients matched on both HER2 and HR status, and 94% of patients matched with the EMR on metastatic and recurrence status. When surgery and treatment information was included with these features, only 57% of patients matched across all these characteristics. Similar concordance was observed between the App questionnaire and EMR. Excluding the 21% of patients reporting “unsure” HER2 status improved the concordance to 85%. Overall concordance of recurrent or metastatic status was higher than for receptor status. Despite the discordance between EMR and patient-reported disease information, 97% of patients reported that they somewhat or strongly understood their cancer diagnosis. A similar pattern of concordance between the App questionnaire and EMR was observed among a real-world cohort of 636 patients using the Outcomes4Me App who provided medical record access. Conclusion: Self report of hormone receptor and HER2 status had limited concordance with the EMR, in contrast to a high degree of accuracy for self-report of metastatic disease. The limited accuracy of self-report suggests a need for improved patient education regarding their cancer characteristics and a need for caution when relying on self-report for clinical trials matching and targeted patient education. The use of a digital platform that integrates self-report with medical record access may help address these critical needs impacting patient empowerment and care. Concordance Between App Questionnaire, Study Survey and EMR (% of patients)Disease Characteristic Matching CriteriaApp v. EMR (n=85)Survey v. EMR (n=107)App Real World Cohort (n=636)HER2 Status73%66%79%HR Status80%85%80%Combined Receptor Status67%62%73%Metastatic Status94%(n=79)97%(n=98)94%Surgery History83%(n=47)95%96%(n=310)Recurrent Status98%(n=48)97%(n=98)98%(n=411)Recurrent/Metastatic Status93%(n=42)94%(n=98)98%(n=411)Receptor/Recurrent Metastatic Status and Surgery History74%(n=33)57%(n=93)70%(n=201) Citation Format: Steven J Isakoff, Eva Glieberman, Maya Said, Agnes H. Kwak, Emily A. O’Rourke, Amanda Stroiney, Laura Spring, Beverly Moy, Aditya Bardia, Nora Horick, Jeffrey Peppercorn. Accuracy of Patient Self-Reported Breast Cancer Disease Characteristics Compared to the Medical Record in a Trial of the Outcomes4MeDigital Health App [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 P4-12-08.

Background: Immunotherapy with checkpoint inhibition is active in mTNBC. Both pembrolizumab and atezolizumab are FDA approved for programmed cell death ligand 1 positive (PDL1+) mTNBC. Vaccines may further induce host immune response and enhance therapeutic activity of checkpoint inhibitors. PVX-410 (PVX) (OncoPep, Inc.) is a novel, HLA-A2 restricted, tetra-peptide vaccine, with 3 of its 4 antigens (XBP1[2 splice variants] and CD138) commonly overexpressed in TNBC. We present results from a phase 1b study evaluating the immune response, safety and tolerability, and clinical activity of PVX and pembrolizumab (PEM) in mTNBC. Methods: Eligibility for this phase 1b multi-center, single-arm study included HLA-A2+, PD-L1 unselected female patients (pts) ≥18 years with metastatic or inoperable locally advanced TNBC, measurable disease, and any number of prior therapies, including prior checkpoint inhibitor therapy. Pts received 6 doses of 800µg PVX emulsified in Montanide ISA 720 VG by subcutaneous injection co-administered with intramuscular Hiltonol weekly for 6 weeks (wks) followed by booster vaccine doses at wks 10 and 28, with concurrent intravenous 200 mg PEM every 3 wks starting with the second PVX dose. Therapy was given until progressive disease, unacceptable toxicity or a maximum of 24 months. Blood samples were scheduled for immune response assessment at baseline and at weeks 2, 5, 10, 28, and 52 post-treatment initiation. The primary objective was PVX- specific immune response at week 10. Immune response was defined as a ≥2-fold change over baseline in the proportion of CD3+CD8+ T cells that expressed IFNγ and the proportion of CD3+CD8+ T cells positive for PVX tetramers following an in vitro stimulation of PBMC with PVX peptides using a flow cytometric assay. Secondary objectives were immune response at wk 28, safety and tolerability, and clinical endpoints (RR, CBR, DCR, DoR, PFS, and OS). Results: Between 3/2018 and 8/2020, 19 pts enrolled. Median age was 62 yrs (range 46-79), with median 2 (range 0-9) lines of prior therapy for metastatic disease. Median disease-free interval among 16 pts with prior early TNBC was 3.3 years. Among 19 enrolled patients, 16 were available for analysis at the time of abstract submission. Among the 16, 10 pts were evaluable at week 10 and 7(70%) demonstrated a PVX specific immune response. There were 6 patients who progressed before week 10, of whom 3 (50%) had a positive immune response at the EOT visit. Immune response persisted in all evaluable pts assessed at week 28 (n=4). Immune response data for all evaluable patients will be updated at the presentation. Among 19 patients evaluable for safety analysis, the most common adverse events (AEs) attributable to PVX (grade ≥2) included: fatigue (21%), arthralgia (11%) injection site reaction (5 %) pain (5%) lymphocyte count decreased (5%), maculopapular rash (5%) and skin infection (5%) . There were two grade 3 AEs attributed to PEM (AST elevation, hyponatremia) and one grade 4 AE (ALT elevation). There were no grade 5 AEs. The clinical benefit rate (CR+PR+SD for ≥16 weeks) was 31.6% with no confirmed partial or complete responses. Best overall response was SD in 9 (47%) patients. Analysis of additional clinical endpoints including PFS and OS is ongoing and will be presented at the meeting. Conclusions: PVX plus PEM is safe with manageable toxicity in pts with mTNBC. No new unexpected adverse events were identified. Immune response data show PVX induces antigen-specific T cell expansion as observed by increases in PVX tetramer and IFN positive T cells. Clinical disease control was observed with a CBR of 31.6%. Based on these promising immune response results in this pretreated population, a phase 2 study with PVX+PEM in combination with standard chemotherapy in treatment naïve, PD-L1+ mTNBC is underway (NCT04634747). Citation Format: Steven J Isakoff, Nadine M. Tung, Jun Yin, Nabihah Tayob, Joanne Parker, Julie Rosenberg, Aditya Bardia, Laura Spring, Hannah Park, Maya Collins, William T. Barry, Mariano Severgnini, Doris Peterkin, Sara M. Tolaney. A phase 1b study of PVX-410 vaccine in combination with pembrolizumab 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 P2-14-17.

PURPOSE The immunogenicity and reactogenicity of SARS-CoV-2 vaccines in patients with cancer are poorly understood. METHODS We performed a prospective cohort study of adults with solid-organ or hematologic cancers to evaluate anti–SARS-CoV-2 immunoglobulin A/M/G spike antibodies, neutralization, and reactogenicity ≥ 7 days following two doses of mRNA-1273, BNT162b2, or one dose of Ad26.COV2.S. We analyzed responses by multivariate regression and included data from 1,638 healthy controls, previously reported, for comparison. RESULTS Between April and July 2021, we enrolled 1,001 patients; 762 were eligible for analysis (656 had neutralization measured). mRNA-1273 was the most immunogenic (log10 geometric mean concentration [GMC] 2.9, log10 geometric mean neutralization titer [GMT] 2.3), followed by BNT162b2 (GMC 2.4; GMT 1.9) and Ad26.COV2.S (GMC 1.5; GMT 1.4; P < .001). The proportion of low neutralization (< 20% of convalescent titers) among Ad26.COV2.S recipients was 69.9%. Prior COVID-19 infection (in 7.1% of the cohort) was associated with higher responses ( P < .001). Antibody titers and neutralization were quantitatively lower in patients with cancer than in comparable healthy controls, regardless of vaccine type ( P < .001). Receipt of chemotherapy in the prior year or current steroids were associated with lower antibody levels and immune checkpoint blockade with higher neutralization. Systemic reactogenicity varied by vaccine and correlated with immune responses ( P = .002 for concentration, P = .016 for neutralization). In 32 patients who received an additional vaccine dose, side effects were similar to prior doses, and 30 of 32 demonstrated increased antibody titers (GMC 1.05 before additional dose, 3.17 after dose). CONCLUSION Immune responses to SARS-CoV-2 vaccines are modestly impaired in patients with cancer. These data suggest utility of antibody testing to identify patients for whom additional vaccine doses may be effective and appropriate, although larger prospective studies are needed.

Supplemental Table S2. Characteristics of patients who underwent both cfDNA and tumor tissue genotyping testing.

Supplemental Figure S1. Consort diagram of patients included in this study.

Supplemental tables

MAF of mutations detected

Purpose:Plasma genotyping may identify mutations in potentially “actionable” cancer genes, such as BRCA1/2, but their clinical significance is not well-defined. We evaluated the characteristics of somatically acquired BRCA1/2 mutations in patients with metastatic breast cancer (MBC).Experimental Design:Patients with MBC undergoing routine cell-free DNA (cfDNA) next-generation sequencing (73-gene panel) before starting a new therapy were included. Somatic BRCA1/2 mutations were classified as known germline pathogenic mutations or novel variants, and linked to clinicopathologic characteristics. The effect of the PARP inhibitor, olaparib, was assessed in vitro, using cultured circulating tumor cells (CTCs) from a patient with a somatically acquired BRCA1 mutation and a second patient with an acquired BRCA2 mutation.Results:Among 215 patients with MBC, 29 (13.5%) had somatic cfDNA BRCA1/2 mutations [nine (4%) known germline pathogenic and rest (9%) novel variants]. Known germline pathogenic BRCA1/2 mutations were common in younger patients (P = 0.008), those with triple-negative disease (P = 0.022), and they were more likely to be protein-truncating alterations and be associated with TP53 mutations. Functional analysis of a CTC culture harboring a somatic BRCA1 mutation demonstrated high sensitivity to PARP inhibition, while another CTC culture harboring a somatic BRCA2 mutation showed no differential sensitivity. Across the entire cohort, APOBEC mutational signatures (COSMIC Signatures 2 and 13) and the “BRCA” mutational signature (COSMIC Signature 3) were present in BRCA1/2-mutant and wild-type cases, demonstrating the high mutational burden associated with advanced MBC.Conclusions:Somatic BRCA1/2 mutations are readily detectable in MBC by cfDNA analysis, and may be present as both known germline pathogenic and novel variants.

Purpose:Actionable mutations can guide genotype-directed matched therapy. We evaluated the utility of tissue-based and plasma-based genotyping for the identification of actionable mutations and selection of matched therapy in patients with metastatic breast cancer (MBC).Experimental Design:Patients with MBC who underwent tissue genotyping (institutional platform, 91-gene assay) or plasma-based cell-free DNA (cfDNA, Guardant360, 73-gene assay) between January 2016 and December 2017 were included. A chart review of records to identify subtype, demographics, treatment, outcomes, and tissue genotyping or cfDNA results was performed. The incidence of actionable mutations and the selection of matched therapy in tissue genotyping or cfDNA cohorts was determined. The impact of matched therapy status on overall survival (OS) in tissue genotyping or cfDNA subgroups was determined with Cox regression analysis.Results:Of 252 patients who underwent cfDNA testing, 232 (92%) had detectable mutations, 196 (78%) had actionable mutations, and 86 (34%) received matched therapy. Of 118 patients who underwent tissue genotyping, 90 (76%) had detectable mutations, 59 (50%) had actionable mutations, and 13 (11%) received matched therapy. For cfDNA patients with actionable mutations, matched versus nonmatched therapy was associated with better OS [HR 0.41, 95% confidence interval (CI): 0.23–0.73, P = 0.002], and this remained significant in a multivariable analysis correcting for age, subtype, visceral metastases, and brain metastases (HR = 0.46, 95% CI: 0.26–0.83, P = 0.010).Conclusions:Plasma-based genotyping identified high rates of actionable mutations, which was associated with significant application of matched therapy and better OS in patients with MBC.See related commentary by Rugo and Huppert, p. 3275

PURPOSE This guideline updates recommendations of the ASCO guideline on chemotherapy and targeted therapy for patients with human epidermal growth factor receptor 2–negative metastatic breast cancer (MBC) that is either endocrine-pretreated or hormone receptor (HR)–negative. METHODS An Expert Panel conducted a targeted systematic literature review guided by a signals approach to identify new, potentially practice-changing data that might translate into revised guideline recommendations. RESULTS The Expert Panel reviewed abstracts from the literature review and retained 14 articles. RECOMMENDATIONS Patients with triple-negative, programmed cell death ligand-1–positive MBC may be offered the addition of immune checkpoint inhibitor to chemotherapy as first-line therapy. Patients with triple-negative, programmed cell death ligand-1–negative MBC should be offered single-agent chemotherapy rather than combination chemotherapy as first-line treatment, although combination regimens may be offered for life-threatening disease. Patients with triple-negative MBC who have received at least two prior therapies for MBC should be offered treatment with sacituzumab govitecan. Patients with triple-negative MBC with germline BRCA mutations previously treated with chemotherapy may be offered a poly (ADP-ribose) polymerase inhibitor rather than chemotherapy. Patients with HR-positive human epidermal growth factor receptor 2–negative MBC for whom chemotherapy is being considered should be offered single–agent chemotherapy rather than combination chemotherapy, although combination regimens may be offered for highly symptomatic or life-threatening disease. Patients with HR-positive MBC with disease progression on an endocrine agent may be offered treatment with either endocrine therapy with or without targeted therapy or single-agent chemotherapy. Patients with HR-positive MBC with germline BRCA mutations no longer benefiting from endocrine therapy may be offered a poly (ADP-ribose) polymerase inhibitor rather than chemotherapy. No recommendation regarding when a patient's care should be transitioned to hospice or best supportive care alone is possible. Additional information is available at www.asco.org/breast-cancer-guidelines .

Immune checkpoint inhibitors (ICIs) have minimal therapeutic effect in hormone receptor-positive (HR+ ) breast cancer. We present final overall survival (OS) results (n = 88) from a randomized phase 2 trial of eribulin ± pembrolizumab for patients with metastatic HR+ breast cancer, computationally dissect genomic and/or transcriptomic data from pre-treatment tumors (n = 52) for molecular associations with efficacy, and identify cytokine changes differentiating response and ICI-related toxicity (n = 58). Despite no improvement in OS with combination therapy (hazard ratio 0.95, 95% CI 0.59–1.55, p = 0.84), immune infiltration and antigen presentation distinguished responding tumors, while tumor heterogeneity and estrogen signaling independently associated with resistance. Moreover, patients with ICI-related toxicity had lower levels of immunoregulatory cytokines. Broadly, we establish a framework for ICI response in HR+ breast cancer that warrants diagnostic and therapeutic validation. ClinicalTrials.gov Registration: NCT03051659., A randomized phase 2 clinical trial has recently shown no benefit of the combination eribulin and pembrolizumab over pembrolizumab alone in HR + metastatic breast cancer patients (NCT03051659). Here, the authors are reporting the final OS data and biomarker analyses on a subset of samples to analyze molecular correlates

In metastatic hormone receptor-positive breast cancer, ESR1 mutations are a common cause of acquired resistance to the backbone of therapy, estrogen deprivation by aromatase inhibition. How these mutations affect tumor sensitivity to established and novel therapies are active areas of research. These therapies include estrogen receptor-targeting agents, such as selective estrogen receptor modulators, covalent antagonists, and degraders (including tamoxifen, fulvestrant, and novel agents), and combination therapies, such as endocrine therapy plus CDK4/6, PI3K, or mTORC1 inhibition. In this review, we summarize existing knowledge surrounding the mechanisms of action of ESR1 mutations and roles in resistance to aromatase inhibition. We then analyze the recent literature on how ESR1 mutations affect outcomes in estrogen receptor-targeting and combination therapies. For estrogen receptor-targeting therapies such as tamoxifen and fulvestrant, ESR1 mutations cause relative resistance in vitro but do not clearly lead to resistance in patients, making novel agents in this category promising. Regarding combination therapies, ESR1 mutations nullify any aromatase inhibitor component of the combination. Thus, combinations using endocrine alternatives to aromatase inhibition, or combinations where the non-endocrine component is efficacious as monotherapy, are still effective against ESR1 mutations. These results emphasize the importance of investigating combinatorial resistance, challenging as these efforts are. We also discuss future directions and open questions, such as studying the differences among distinct ESR1 mutations, asking how to adjust clinical decisions based on molecular surveillance testing, and developing novel therapies that are effective against ESR1 mutations.

Enhanced understanding of the molecular events underlying oncogenesis has led to the development of “tumor‐agnostic” treatment strategies, which aim to target a tumor's genomic profile regardless of its anatomic site of origin. A classic example is the translocation resulting in an ETV6‐NTRK3 gene fusion, a characteristic driver of a histologically diverse array of cancers. The chimeric ETV6‐NTRK3 fusion protein elicits constitutive activation of the tropomyosin receptor kinase (TRK) C protein, leading to increased cell survival, growth, and proliferation. Two TRK inhibitors, larotrectinib and entrectinib, are currently approved for use in the metastatic setting for the treatment of advanced solid tumors harboring NTRK fusions. Here we report a rare case of recurrent secretory carcinoma of the breast (SCB) with NTRK3 gene fusion. Whereas most cases of SCB represent slow‐growing tumors with favorable outcomes, the case detailed here is the first to the authors' knowledge of recurrence within 1 year of surgery. We review the molecular findings and potential clinical significance. KEY POINTS: The translocation resulting in the ETV6‐NTRK3 gene fusion is a known oncogenic driver characteristic of secretory carcinoma of the breast (SCB). Whereas most cases of SCB represent slow‐growing tumors with favorable outcomes, the case here with ETV6‐NTRK3 gene fusion had local recurrence within 1 year of surgery. Two tropomyosin receptor kinase (TRK) inhibitors, larotrectinib and entrectinib, are approved to treat NTRK fusion–positive tumors, demonstrating sustained high overall response rates in the metastatic setting. Approval of TRK inhibitors necessitates optimization of NTRK fusion detection assays, including detection with liquid biopsies.

Patients with metastatic triple-negative breast cancer have a poor prognosis. Sacituzumab govitecan (IMMU-132) is an antibody-drug conjugate that contains the irinotecan active metabolite, SN-38, linked to a humanized monoclonal antibody targeting trophoblast cell surface antigen 2, which is overexpressed in many solid tumors. In a basket design phase I/II study, sacituzumab govitecan demonstrated promising single-agent therapeutic activity in multiple cancer cohorts, leading to accelerated approval by the U.S. Food and Drug Administration of sacituzumab govitecan-hziy (TRODELVY) for the treatment of patients with metastatic triple-negative breast cancer who had received at least two prior therapies in the metastatic setting. Recently, results of the phase III trial, ASCENT, were confirmatory. There is limited available information on the adverse event management with sacituzumab govitecan needed to maximize the dose and duration of effective therapy while maintaining patient quality of life. This review summarizes the clinical development and the practical management of patients receiving sacituzumab govitecan. Sacituzumab govitecan has a well-defined and manageable toxicity profile, and rapid recognition and appropriate early and proactive management will allow clinicians to optimize sacituzumab govitecan treatment for patients.Implications for PracticeSacituzumab govitecan (TRODELVY) is a novel antibody-drug conjugate composed of the active metabolite of irinotecan (SN-38) conjugated to a monoclonal antibody targeting trophoblast cell surface antigen 2, an epithelial cell surface antigen overexpressed in many cancers. Because of the rapid approval of sacituzumab govitecan, there is limited available information on adverse event (AE) management with this agent. As such, this article reviews the clinical development of the drug, the AE profile, and provides recommendations regarding AE management to help optimize therapy with sacituzumab govitecan.

Combining cyclin-dependent kinase (CDK) inhibitors with endocrine therapy improves outcomes for patients with metastatic estrogen receptor-positive breast cancer but its value in earlier-stage patients is unclear. We examined evolutionary trajectories of early-stage breast cancer tumors, using single-cell RNA sequencing of serial biopsies from the FELINE clinical trial of endocrine therapy (letrozole) alone or combined with the CDK inhibitor ribociclib. Despite differences in subclonal diversity evolution across patients and treatments, common resistance phenotypes emerged. Resistant tumors treated with combination therapy showed accelerated loss of estrogen signaling with convergent upregulation of JNK signaling through growth factor receptors. In contrast, cancer cells maintaining estrogen signaling during mono- or combination therapy showed potentiation of CDK4/6 activation and ERK upregulation through ERBB4 signaling. These results indicate that combination therapy in early-stage estrogen receptor-positive breast cancer leads to emergence of resistance through a shift from estrogen to alternative growth signal-mediated proliferation. Bild and colleagues identify convergent clonal evolution mechanisms through single-cell genomic analyses, explaining therapy resistance in patients with early-stage breast cancer treated with endocrine and CDK4/6 therapy in the FELINE trial.

Triple-Negative Breast Cancer (TNBC) is an aggressive breast cancer subset, which lacks expression of estrogen receptors, progesterone receptors, and human epidermal growth factor receptor-2. This subset of breast cancer disproportionately affects Black and African American women and improving TNBC treatment options is vital to reducing breast cancer mortality. The novel antibody-drug conjugate, Sacitizumab Govetican (SG), which targets TROP2 at the cell surface, has shown promising clinical results from the NeoSTAR trial (NCT04230109), a phase II study evaluating neoadjuvant SG therapy in a localized TNBC setting. As part of the NeoSTAR clinical trial, we have collected and processed pre- and post- SG treatment patient samples, with the aim of understanding response to this monotherapy. Herein, we identify biomarkers of response and resistance to SG monotherapy through the use of single cell RNA sequencing of matched pre- and post-treatment patient biopsies combined with exome sequencing these patient samples. Pre-treatment core needle biopsy samples, and if applicable, post-treatment residual disease biopsies were dissociated into single cell suspensions and subjected to single cell RNA sequencing. Additionally, fixed patient tissue samples were processed accordingly for exome sequencing analyses. Overall, we analyzed over 144,000 cells from 37 total scRNA seq libraries with an average of 3800 cells per biopsy sample, demonstrating the feasibility of this method. From these analyses, we observed several cell-type differences between patients who achieved a pathological complete response (pCR) and patients who had residual disease (RD). Specifically, our data shows that tumor infiltrating lymphocytes are a potential prognostic biomarker of response to SG. Furthermore, we detected alterations in among stromal and immune cell subsets, among non-responders, indicating that these cell types maybe indicative of SG resistance. Taken together, we outline biomarkers of response to SG treatment for an improved understanding of resistance mechanisms in the neoadjuvant setting to improve TNBC outcomes among patients. Citation Format: Nicole Peiris, Simona Cristea, Mengran Zhang, Siang Koh, James Coates, Ilze Smidt, Veerle Bossuyt, Laura Spring, Aditya Bardia, Leif Ellisen. Utilizing scRNA sequencing to understand biomarkers of response and resistance to Sacitizumab Govetican in localized TNBC. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4353.

Purpose: Plasma genotyping may identify mutations in potentially “actionable” cancer genes, such as BRCA1/2, but their clinical significance is not well-defined. We evaluated the characteristics of somatically acquired BRCA1/2 mutations in patients with metastatic breast cancer (MBC). Experimental Design: Patients with MBC undergoing routine cell-free DNA (cfDNA) next-generation sequencing (73-gene panel) before starting a new therapy were included. Somatic BRCA1/2 mutations were classified as known germline pathogenic mutations or novel variants, and linked to clinicopathologic characteristics. The effect of the PARP inhibitor, olaparib, was assessed in vitro, using cultured circulating tumor cells (CTCs) from a patient with a somatically acquired BRCA1 mutation and a second patient with an acquired BRCA2 mutation. Results: Among 215 patients with MBC, 29 (13.5%) had somatic cfDNA BRCA1/2 mutations [nine (4%) known germline pathogenic and rest (9%) novel variants]. Known germline pathogenic BRCA1/2 mutations were common in younger patients (P = 0.008), those with triple-negative disease (P = 0.022), and they were more likely to be protein-truncating alterations and be associated with TP53 mutations. Functional analysis of a CTC culture harboring a somatic BRCA1 mutation demonstrated high sensitivity to PARP inhibition, while another CTC culture harboring a somatic BRCA2 mutation showed no differential sensitivity. Across the entire cohort, APOBEC mutational signatures (COSMIC Signatures 2 and 13) and the “BRCA” mutational signature (COSMIC Signature 3) were present in BRCA1/2-mutant and wild-type cases, demonstrating the high mutational burden associated with advanced MBC. Conclusions: Somatic BRCA1/2 mutations are readily detectable in MBC by cfDNA analysis, and may be present as both known germline pathogenic and novel variants.

Purpose During the COVID-19 pandemic, most breast surgery for benign and malignant conditions has been postponed, creating a backlog of patients who will need surgery. A fair and transparent system for assessing the risk of further delaying surgery for individual patients to prioritize surgical scheduling is needed. Methods Factors related to risk of delaying surgery for breast patients were identified. Scores were assigned to each factor, with higher scores indicating a greater risk from delaying surgery. REDCap and Microsoft Excel tools were designed to track and score delayed patients. Results Published data and multidisciplinary clinical judgement were used to assign risk scores based on patient and tumor factors, length of delay, and tumor response to preoperative therapy. Patients completing neoadjuvant chemotherapy were assigned the highest scores as their options for delaying surgery are most limited. Among patients receiving neoadjuvant endocrine therapy or no medical therapy, higher scores were assigned for low-estrogen receptor or high-genomic risk scores, higher grade, larger tumors, younger age and longer delay. High priority scores were assigned for progression during preoperative therapy. Low scores were assigned for re-excisions, atypical lesions and other benign indications. There was good agreement of the tool’s ranking of sample patients with rankings by experienced clinicians. The tool generates risk-stratified patient lists by surgeon or institution to facilitate assignment of surgery dates. Conclusions This tool generates a clinically consistent, risk-stratified priority list of breast surgical procedures delayed by the COVID-19 pandemic. This systematic approach may facilitate surgical scheduling as conditions normalize.

A Woman with Early Breast Cancer during the Covid-19 Pandemic A 62-year-old woman was evaluated for a mass that had been identified in the left breast during the Covid-19 pandemic. Mammography reve...

Summary The development and approval of cyclin-dependent kinase (CDK) 4 and 6 inhibitors for hormone receptor-positive and human epidermal growth factor receptor 2 (HER2)-negative metastatic breast cancer represents a major milestone in cancer therapeutics. Three different oral CDK4/6 inhibitors, palbociclib, ribociclib, and abemaciclib, have significantly improved progression-free survival by a number of months when combined with endocrine therapy. More recently, improvement in overall survival has been reported with ribociclib and abemaciclib. The toxicity profile of all three drugs is well described and generally easily manageable with dose reductions when indicated. More myelotoxicity is observed with palbociclib and ribociclib, but more gastrointestinal toxicity is observed with abemaciclib. Emerging data is shedding light on the resistance mechanisms associated with CDK4/6 inhibitors, including cell cycle alterations and activation of upstream tyrosine kinase receptors. A number of clinical trials are exploring several important questions regarding treatment sequencing, combinatorial strategies, and the use of CDK4/6 inhibitors in the adjuvant and neoadjuvant settings, thereby further expanding and refining the clinical application of CDK4/6 inhibitors for patients with breast cancer.

Background: Recent studies in murine models and humans suggest that modulation of the gut microbiome may enhance response to immune checkpoint blockade in different cancer types. However, little is known about the landscape of gut microbiome in pts with HR+ MBC and its influence on response to chemotherapy and immunotherapy.Methods: A randomized phase 2 trial of E +/- P for pts with HR+ MBC (n= 88) was conducted. The results of this study have been previously presented and found the addition of P did not result in an improvement in progression-free survival (PFS). Fecal samples were prospectively collected (baseline (BL), after 2 cycles of therapy (C2), and end of treatment (EOT)) in a subset of pts (E+P, n = 12; E, n = 11) in order to evaluate if microbiome was associated with response (partial response [PR], stable disease [SD], and progressive disease [PD]), PFS, and overall survival (OS). 16S rRNA gene sequencing was performed to characterize the diversity and composition of fecal microbiome. Results: A total 23 pts provided 23 BL, 22 C2, and 5 EOT fecal specimens for microbiome profiling. 16S(v3-4) rRNA gene data was successfully generated for all samples and the dataset was rarefied to 24,743 reads for analysis. Overall, the variability in the composition and structure of the fecal microbiome was significantly driven by each individual (p Conclusion: The composition and structure of the fecal microbiome identified in this study were found to be associated primarily with the pt rather than with any of the variables studied including type of treatment and outcome. Although the fecal microbiome from all pts randomized were indistinguishable at BL, shifts in the abundance of certain types of bacteria like Faecalibacterium and Akkermansia were observed from BL to C2. These shifts were characteristic of pts receiving E but not of those receiving E+P. Although this study is limited by the small sample size in each arm, these findings warrant further evaluation in a larger population to interrogate if the composition and metabolic potential of the fecal microbiome can be used as a predictor of benefit to treatment. Citation Format: Romualdo Barroso de Sousa, Nadim Ajami, Tanya E Keenan, Chelsea Andrews, Jessica L Pittenger, Gerburg Wulf, Laura Spring, Ian E Krop, Eric P Winer, Elizabeth A Mittendorf, Sara M Tolaney. Fecal microbiome and association with outcomes among patients (pts) receiving eribulin (E) +/- pembrolizumab (P) for hormone receptor positive (HR+) metastatic breast cancer (MBC) [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P3-09-16.

Background: Niraparib is a selective poly(ADP-ribose) polymerase 1/2 inhibitor that has demonstrated antitumor activity in advanced triple-negative breast cancer (TNBC) in combination with a programmed cell death 1 inhibitor, with the greatest clinical activity seen in tumors with breast cancer susceptibility gene (BRCA) mutations. Pharmacologically, niraparib has demonstrated a wide volume of distribution and high cell membrane permeability. In breast and ovarian cancer xenograft mouse models, niraparib achieved tumor exposures that were 3.3 times greater than plasma exposure. The objective of this study is to evaluate the antitumor activity of single-agent niraparib in the neoadjuvant treatment of patients with localized, human epidermal growth factor receptor 2 (HER2)-negative, BRCA-mutated breast cancer. The relative concentration of niraparib in tumor versus plasma was also assessed. Methods: Eligible patients were ≥18 years old, with HER2-negative, BRCA-mutated (germline or somatic) resectable breast cancer with a tumor size of ≥1 cm who had not received prior treatment for the current malignancy. Patients received niraparib 200 mg once daily for 2 months. At the end of 2 months, at their treating physician’s discretion, patients proceeded directly to surgery, received additional cycles of niraparib (maximum of 6 months), or received neoadjuvant chemotherapy. The primary endpoint was tumor response rate measured by magnetic resonance imaging (MRI) after 2 months of treatment. Response was defined as a ≥30% reduction in tumor volume from baseline. Secondary endpoints included tumor response rate measured by ultrasound, quantified percent change in tumor volume measured by MRI or ultrasound, pathological complete response, and safety and tolerability. Additionally, niraparib concentrations were measured in tumor and plasma samples using qualified liquid chromatography-tandem mass spectrometry. Results: Twenty-one patients were enrolled. As of June 2019, 18 patients had both an MRI and ultrasound scan at the end of month 2 and were evaluable for response. Ten patients are currently on treatment. The median age of patients was 43 years (range, 21-73). Fourteen patients had a BRCA1 mutation, 6 patients had a BRCA2 mutation, and 1 patient had both. Fifteen patients had TNBC, and 6 patients had hormone receptor-positive disease. All 18 response-evaluable patients had a clinical response after 2 months of treatment by at least one imaging modality; no patient experienced disease progression. Tumor response rate measured by MRI after 2 months of treatment was 89% (n/N = 16/18). Results measured by ultrasound were similar, with a 94% response rate at cycle 2 (n/N = 17/18). The median percent decrease in tumor volume after 2 months of treatment was 88% (range, 26-100%) and 89% (range, 23-100%) as measured by MRI and ultrasound, respectively. In the 5 samples measured thus far, niraparib concentrations in tumor biopsies after 2 months of treatment ranged from approximately 4-131-fold higher than those in corresponding plasma samples. Efficacy and tumor concentration data for all patients will be presented at the meeting. The most common (≥10%) drug-related treatment-emergent adverse events (TEAEs) of any grade were nausea, fatigue, anemia, insomnia, and decreased appetite. The only drug-related grade ≥3 toxicity in ≥10% of patients was anemia (3 patients). Three patients had a dose reduction due to a TEAE; no patient discontinued treatment due to a TEAE. Conclusion: Niraparib was well tolerated and showed promising antitumor activity in the neoadjuvant treatment of patients with localized HER2-negative, BRCA-mutated breast cancer. Niraparib achieved 4-131-fold higher concentrations in tumor than in plasma. Clinical trial information: NCT03329937. Funding: TESARO: A GSK Company (Waltham, MA, USA) sponsored the study. Citation Format: Hyo Han, Minetta C Liu, Erika Hamilton, Hanna Irie, Cesar A Santa-Maria, James Reeves, Andre Liem, Adrianna Milillo Naraine, Julie Nangia, David Page, Meghan Duncan, Ming Shan, Yongqiang Tang, Julie R Graham, Leif W Ellisen, Steven Isakoff, Laura Spring. Pilot neoadjuvant study of niraparib in HER2-negative, BRCA-mutated resectable breast cancer [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P3-11-03.

Background: BM in MBC patients cause significant morbidity and mortality. BRCA1 germline mutations have previously been shown to be associated with an increased risk of developing BM (Lee et al, 2011), with an incidence as high as 15% (Zavitsanos et al, 2016). We previously reported that a subset of MBC patients may have somatic BRCA mutations in the absence of germline BRCA mutations (Vidula N, SABCS, 2017). In this study, we evaluated the incidence and clinical characteristics of BM in MBC patients with somatic BRCA mutations detected by cfDNA. Methods: MBC patients with somatic BRCA1 or 2 mutations detected by cfDNA (Guardant360TM, next generation sequencing, 73 gene panel; mutations classified as somatic by Guardant360TM) with at least 4 months of follow-up post-testing at an academic institution were identified. From this cohort, we identified patients who developed BM post cfDNA testing. A retrospective review of medical records and Guardant360TM reports was conducted to identify demographics, tumor subtype, type of cfDNA BRCA mutation, whether the BRCA mutation was known to be pathogenic, germline BRCA mutation status, mutant allele fraction (MAF), clonality (MAF ratio of BRCA mutation/gene mutation with highest MAF ≥ 0.25 for clonal, and Results: Of 36 MBC patients with somatic BRCA mutations, 9 (25%) developed BM and 27 (75%) did not have BM (non-BM). The median time to development of BM was 6.7 months after cfDNA testing. Of the BM patients, 5 (56%) had triple-negative (TN) and 4 (44%) had hormone receptor positive (HR+)/HER2- MBC in comparison with the non-BM cases where 5 (19%) had TN, 19 (70%) had HR+/HER2-, and 3 (11%) had HER2+ MBC. Very few patients (1 BM and 2 non-BM) had known co-existing separate germline BRCA mutations (rest not known BRCA carriers confirmed by negative germline testing and/or absence of family history suggestive of a germline BRCA phenotype). The median age at MBC diagnosis was similar for BM and non-BM patients (57 years). PIK3CA and TP53 mutations were commonly seen in both BM and non-BM cases. Additionally, MYC, EGFR, and CCNE1 mutations were commonly seen in BM cases. As outlined in Table 1, among patients with BM, the somatic BRCA mutations were commonly BRCA1, clonal, known to be pathogenic (56%), and present at a higher MAF, but these findings did not reach statistical significance possibly due to the small sample size. Brain tumor tissue mutation status in BM patients and correlation with cfDNA results will be presented at the meeting. Conclusions: We observed a relatively high incidence (25%) of BM in MBC patients with somatic BRCA mutations detectable by cfDNA, which were often known to be pathogenic mutations (56%), and often associated with co-existing MYC, EGFR, and CCNE1 mutations. Further research using a larger cohort with adequate statistical power is needed to validate these findings, and may help identify MBC patients at risk for BM using a liquid biopsy. Table 1.Characteristic BMNon-BMPrior anthracycline and/or platinum6 (67%)16 (59%)Type of somatic BRCA mutationBRCA16 (67%)11 (41%)BRCA22 (22%)15 (56%)BRCA1 and 21 (11%)1 (4%)Median BRCA MAF0.40.17ClonalityClonal6 (67%)13 (48%)Subclonal3 (33%)14 (52%)Mutation known to be pathogenic5 (56%)7 (26%)Common co-existing mutationsPIK3CA5 (56%)12 (44%)TP535 (56%)15 (56%)MYC5 (56%)8 (30%)EGFR5 (56%)8 (30%)CCNE15 (56%)6 (22%)KIT3 (33%)5 (19%) Citation Format: Neelima Vidula, Andrzej Niemierko, Giuliana Malvarosa, Priscilla Brastianos, Erica Blouch, Kristen Shannon, Steven Isakoff, Seth Wander, Laura Spring, Jerry Younger, Kristin Price, Beverly Moy, Dejan Juric, Leif Ellisen, Aditya Bardia. Brain metastases (BM) in patients with metastatic breast cancer (MBC) and circulating cell-free DNA (cfDNA) somatic BRCA mutations [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P4-09-06.

Background: The cyclin-dependent 4/6 inhibitors (CDK4/6i), in combination with an anti-estrogen, have emerged as the standard of care for patients with HR+/HER2- MBC. While only limited insight exists into the molecular factors that drive progression, emerging evidence suggests that activation of AKT1 may provoke resistance in a subset of patients. Overexpression of AKT1 also conveys resistance in HR+/HER2- breast cancer cells in vitro. AKT1 plays a well-established role in promoting tumor progression and metastasis. Targeting AKT1 following progression on CDK4/6i may provide durable clinical benefit in HR+/HER2- MBC. Trial Design: This is an open-label phase Ib trial with three arms - Arm A includes fulvestrant + ipatasertib and Arm B includes an aromatase inhibitor (AI) + ipatasertib. Arm C includes fulvestrant + ipatasertib + palbociclib. Arm A and B are dose-expansion cohorts while Arm C is a dose-escalation (standard 3+3 design) followed by subsequent dose-expansion. Eligibility Criteria: Key inclusion criteria include the presence of locally advanced/unresectable and metastatic HR+/HER2- breast cancer; postmenopausal status or pre/peri-menopausal status s/p oophrectomy or GNRH agonist; at least one prior therapy for MBC including any CDK4/6i; adequate performance status (ECOG 0-2); and adequate bone marrow and hepatic function. Stable CNS metastatic disease and up to two prior lines of chemotherapy for MBC are allowed (no limit on number of prior lines of endocrine therapy). Key exclusion criteria include prior use of fulvestrant (for Arm A); any prior intolerable toxicity with CDK4/6i (for Arm C); prior exposure to an AKT inhibitor in any setting; active CNS disease; concurrent use of specific CYP3A4 inhibitors or inducers; poorly controlled intercurrent illness; and pregnancy or active child-bearing potential. Specific Aims: The primary objective of this study is to evaluate the safety and tolerability of ipatasertib in combination with endocrine therapy (aromatase inhibitor or fulvestrant) with or without CDK4/6i in patients with HR+/HER2- MBC who have received prior CDK 4/6i. Secondary objectives include assessment of objective response rate (ORR), clinical benefit rate (CBR), and progression free survival (PFS). Exploratory objectives include next generation sequencing of solid tumor biopsies and cfDNA along with immunohistochemical analysis of tumor biopsies to identify genomic and protein-based predictors of response and resistance. Statistical Methods: Arms A and B constitute dose-expansion cohorts to confirm the safety/tolerability of ipatasertib use with anti-estrogens and evaluate preliminary efficacy. A dose-limiting toxicity (DLT) rate of Present and Target Accrual: Anticipated accrual for Arms A+B will be n=15 (each). Arm C enrollment will be n=15-30 pending establishment of RP2D/MTD prior to dose expansion. Current enrollment n=4, since study activation in May 2019. Citation Format: Seth A. Wander, Dejan Juric, Laura M. Spring, Neelima Vidula, Maureen Beeler, Karleen Habin, Elene Viscosi, Lauren Scarpetti, Elizabeth Tripp, Rachel Hepp, Beverly Moy, Steven J. Isakoff, Leif W. Ellisen, Aditya Bardia. A phase 1b trial to evaluate safety and anti-tumor activity of the AKT inhibitor, ipatasertib, in combination with endocrine therapy with/without CDK 4/6 inhibitor for patients with hormone receptor positive (HR+)/HER2 negative metastatic breast cancer (MBC) (TAKTIC) [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr OT2-08-01.

Background: The comprehensive analysis of clinically annotated tissue specimens from those with either benign, high risk or malignant breast findings is critical to improve the understanding of breast cancer biology and treatment. Through a multidisciplinary team approach, we designed a protocol to allow a breast research biopsy to be collected with informed patient consent concurrent with the diagnostic biopsy at our institution. Here we describe the feasibility of the project. Methods: IRB approval was obtained for the prospective collection and storage of clinically-annotated specimens, including breast biopsy cores, excess surgical tissue from breast surgery, and optional blood collection. Potential participants are identified through the list of scheduled breast biopsies at the Massachusetts General Hospital breast imaging center. Eligible patients are those ≥ age 18 undergoing a clinical breast biopsy. Research consent is obtained in the procedure room immediately following the clinical consent process and prior to the clinical biopsy. Following completion of standard clinical biopsy workflow, two research core biopsy specimens are obtained with a core biopsy needle ranging from 9 to 18 gauge. The first research specimen is flash frozen and stored on dry ice to preserve high molecular weight DNA and RNA. The second sample is cryopreserved in DMSO or a related agent to allow viable cell recovery. All consented patients are entered into a prospective database in REDCap. Medical records of the participating patients are reviewed periodically to collect data on patient demographics, tumor characteristics, and long-term outcomes. Results: From 1/17/19 through 6/28/19, 144 patients were approached. 77.8% of patients consented, resulting in 96 lesions being biopsied for research. Of these, 45.8% were invasive carcinoma, 3.1% were DCIS, 6.1% were high risk lesions, and 44.8% were benign. Among the invasive breast cancers, 78.6% were hormone receptor-positive (HR+) and human epidermal growth factor receptor 2-negative (HER2-), 9.5% were HER2+, and 11.9% were triple negative. Conclusion: We demonstrated that an upfront breast research biopsy program in patients presenting for initial diagnostic breast biopsy is feasible, with high rates of patient participation. Overall, 77.8% of approached subjects agreed to a concurrent research breast biopsy at the time of diagnostic biopsy. This approach may provide a high yield mechanism to generate a rich tissue repository with low cost and marginal additional time commitment by patient and providers that can support novel, cross-disciplinary research. A number of collaborative research projects are planned. Citation Format: Kassidy Beyerlin, Christine Edmonds, Siang Boon Koh, Veerle Bossuyt, Annie Ma, Rachel Jimenez, Michelle Specht, Barbara L Smith, Brian Dontchos, Dennis Sgroi, Steven J Isakoff, Constance Lehman, Leif W Ellisen, Laura M Spring. Feasibility of a multidisciplinary diagnostic breast research biopsy project [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P2-21-01.

Retrospective analysis of nightly fasting among women with breast cancer suggests that fasting 13 h may be associated with a higher risk of breast cancer recurrence. We sought to evaluate prolonged overnight fasting (POF), an accessible nonpharmacological intervention, in a prospective feasibility study.We designed a single-arm, pilot study to evaluate the feasibility of fasting for 13 h overnight for 12 weeks among women with a history of early-stage breast cancer survivors. Baseline and end of study assessments included measurements of body mass index (BMI), blood biomarkers, quality of life (QOL), mood, fatigue, and physical activity. Patient-reported outcome questionnaires were also administered at 6 weeks. Feasibility was defined as ≥ 60% of participants documenting fasting for 13 h on at least 70% of nights during the study period.Forty women with a history of breast cancer were enrolled with a median age of 60 (range 35-76) and median time since diagnosis of 4.5 years (range 0.8-20.7). At baseline, BMI was ≥ 25 in 37.5%. Ninety-five percent of participants fasted ≥ 13 h for at least 70% of study days (95% CI 83-99%). There was a statistically significant improvement in anxiety (p = 0.0007) at 6 weeks and BMI (p = 0.0072), anxiety (p = 0.0141), depression (p = 0.0048), and fatigue (p = 0.0105) at 12 weeks. There was no significant change in overall QOL, physical activity levels, or blood biomarkers at 12 weeks.POF is feasible among patients with a history of breast cancer and may potentially improve BMI, mood, and fatigue without detrimental effects on overall QOL.

PURPOSE Accurate monitoring of therapeutic response remains an important unmet need for patients with metastatic breast cancer (MBC). Analysis of tumor genomics obtained via circulating tumor DNA (ctDNA) can provide a comprehensive overview of tumor evolution. Here, we evaluated ctDNA change as an early prognostic biomarker of subsequent radiologic progression and survival in MBC. PATIENTS AND METHODS Paired blood samples from patients with MBC were analyzed for levels of ctDNA, carcinoembryonic antigen, and cancer antigen 15-3 at baseline and during treatment. A Clinical Laboratory Improvement Amendments–certified sequencing panel of 73 genes was used to quantify tumor-specific point mutations in ctDNA. Multivariable logistic regression analysis was conducted to evaluate the association between ctDNA rise from baseline to during-treatment (genomic progression) and subsequent radiologic progression and progression-free survival (PFS). RESULTS Somatic mutations were detected in 76 baseline samples (90.5%) and 71 during-treatment samples (84.5%). Patients with genomic progression were more than twice as likely to have subsequent radiologic progression (odds ratio, 2.04; 95% CI, 1.74 to 2.41; P < .0001), with a mean lead time of 5.8 weeks. Genomic assessment provided a high positive predictive value of 81.8% and a negative predictive value of 89.7%. The subset of patients with genomic progression also had shorter PFS (median, 4.2 v 8.3 months; hazard ratio, 2.97; 95% CI, 1.75 to 5.04; log-rank P < .0001) compared with those without genomic progression. CONCLUSION Genomic progression, as assessed by early rise in ctDNA, is an independent biomarker of disease progression before overt radiologic or clinical progression becomes evident in patients with MBC.

Antibody-drug conjugates (ADCs) are composed of monoclonal antibodies linked to a cytotoxic payload, enabling targeted delivery of more potent chemotherapy. In the past decade, there has been rapid development of ADCs aimed at different types of breast cancer. The success of the monoclonal antibody trastuzumab has led to the evolution of several antibody-drug conjugates targeting HER2-positive breast cancer. Trastuzumab-emtansine (T-DM1), the first approved ADC targeting HER2-positive breast cancer, has become standard of care for patients with high-risk early-stage HER2-positive breast cancer who have residual disease after neoadjuvant chemotherapy. More recently, the observation of the bystander effect, in which ADCs target both antigen-positive cells and adjacent antigen-negative cells, has led to the reclassification of “HER2-low” breast cancer and the development of trastuzumab-deruxtecan (T-DXd) to target this population. This article reviews the history of HER2-directed ADCs in breast cancer as well as ongoing ADCs in development.

Background: De-escalation of adjuvant therapy following pathologic complete response (pCR) to an abbreviated neoadjuvant regimen in HER2-positive (HER2+) breast cancer is the focus of a recently initiated national trial. However the feasibility of this approach, and its appeal to patients (pts) and providers, has not been formally investigated. Methods: We conducted a single arm pilot trial to determine the feasibility of de-escalated adjuvant therapy (HP-only) in patients with pCR following neoadjuvant THP. Eligible pts had clinical anatomic stage II-III treatment-naïve HER2+ breast cancer. All pts received weekly paclitaxel x12 doses, and HP every 3 weeks x4 doses (up to 6 doses allowed in case of surgical delay). The primary objective was to assess adherence to protocol-specified antibody doublet therapy (HP-only, without cytotoxic chemotherapy) in the adjuvant setting among pts with pCR (ypT0/isN0) following neoadjuvant THP; the primary endpoint was receipt of adjuvant cytotoxic chemotherapy, assessed 3 months post-operatively. Trastuzumab emtansine (T-DM1) was not considered cytotoxic chemotherapy. Among pts with pCR to THP, de-escalation would be deemed infeasible if the true rate of adherence to HP-only were 90% power to reject the null if the true rate of adherence were >95% (Binomial exact test; one-sided alpha=0.05). Questionnaires were administered and records were reviewed to assess pts’ and physicians’ decision-making about adjuvant systemic therapy following pCR and non-pCR. Results: 98 pts received at least one dose of THP on study. Median age was 50 yrs (range 24-78), pts were 99% female, 86% had stage II/14% stage III tumors, 32% ER/PR negative. No pts progressed during neoadjuvant THP. Five pts had incomplete clinical response following THP and received AC prior to surgery. They were classified as non-pCR and censored from further analyses. At the time of analysis, 93 pts were evaluable for response to neoadjuvant therapy (1 pt withdrew from study early; 4 pts had not reached surgery by the data cutoff). Overall pCR rate was 55% (51/93 pts); 10%, 28%, and 2% of pts had RCB I, II, and III responses, respectively (this excluded patients who received AC preoperatively). Of 51 pts who had pCR to THP, 40 had verified data available regarding adjuvant chemotherapy receipt at data cutoff. 39/40 pts (97.5%, 95% CI 86.8-99.9%) who had pCR did not receive adjuvant cytotoxic chemotherapy, meeting the trial’s prespecified threshold for declaring this a feasible approach (primary endpoint), though data remain pending for 11 pts with pCR and will be available at presentation. Of 30 pts who did not experience pCR to THP and had adjuvant chemotherapy status verified at data cutoff, 14/30 pts received adjuvant cytotoxic chemotherapy, and 16/30 pts did not receive adjuvant chemotherapy. The most common reasons cited by pts for non-receipt of adjuvant cytotoxic chemotherapy, despite residual disease at surgery, were (N=21): plan for adjuvant T-DM1 alone (67% of pts), good response to preop chemo (38% of pts), and plan for adjuvant hormonal therapy (24% of pts). The most common reason cited by treating physicians for non-administration of adjuvant chemotherapy, despite residual disease at surgery, was plan for adjuvant T-DM1 (17/21 (81%) physicians). With brief follow-up (median 10.2 mos), there were no breast cancer recurrences. Conclusions: De-escalation of adjuvant cytotoxic chemotherapy among pts who experience pCR in early stage HER2+ breast cancer appears to be an acceptable approach for both pts and physicians, though data are not yet complete and will be updated at the time of presentation. The long-term efficacy of this approach will be determined in the ongoing national CompassHER2-pCR trial. Citation Format: Adrienne G. Waks, Neelam V. Desai, Tianyu Li, Philip D. Poorvu, Ann H. Partridge, Natalie Sinclair, Laura M. Spring, Meredith Faggen, Michael Constantine, Jillian C. Alberti, Julia Deane, Shoshana M. Rosenberg, Sara M. Tolaney, Ian E. Krop, Nadine M. Tung, Nabihah Tayob, Tari A. King, Elizabeth A. Mittendorf, Eric P. Winer. The DAPHNE trial: A feasibility study of chemotherapy de-escalation based on response to neoadjuvant paclitaxel-HP (THP) in HER2-positive 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 PD3-05.

422 Background: ALP is a PI3Kα inhibitor and degrader approved with fulvestrant for the treatment (tx) of patients (pts) with PIK3CA-mutated, HR+, HER2– ABC. Hyperglycemia (HG) and rash are expected adverse events with ALP tx and remain a challenge for physicians and pts. Management guidance is primarily based on clinical trial experience, which is not necessarily reflective of real-world pts. Here we report guidance for optimizing prevention and management of HG and rash in pts taking ALP based on an integrated Delphi panel, a systematic, validated approach to organize consensus from experts in the absence of definitive evidence. Methods: Two modified Delphi panels were conducted, focusing on HG and rash, respectively. Each panel included 4 oncologists, 4 endocrinologists or dermatologists, 1 clinical pharmacist, and 1 pt advocate. Experts were asked to rate appropriateness of 908 interventions for HG and 348 for rash on hypothetical pt scenarios on a 1 (highly inappropriate) to 9 (highly appropriate) scale. Results were reviewed at virtual meetings, after which experts repeated the rating. The level of agreement or disagreement was determined using the median scores and dispersion from the final rating, and this level of agreement was used to develop consensus statements and tx algorithms. Results: Per the HG panel, (a) ALP tx is appropriate in individuals with HbA1c 6.5% to < 8% with a pre-tx endocrinology consult; (b) low carbohydrate diet is appropriate in all pts starting ALP; (c) prophylactic metformin is appropriate in pts with baseline HbA1c 5.7%-6.4%; may also be appropriate in pts with HbA1c < 5.7%; (d) after metformin, an SGLT2 inhibitor or a thiazolidinedione is an appropriate second-/third-line anti-HG agent (or first-line in metformin-intolerant pts), while insulin is not. Per the rash panel, (a) prophylactic nonsedating (NS) H1 antihistamines (standard dose) are appropriate for all pts; (b) starting/escalating NS H1 antihistamines and topical steroids (TS) is the preferred first step for managing rash; (c) it is appropriate to add, but not replace with, a sedating H1 antihistamine, if response to high-dose, NS option is inadequate, and to add an H2 antihistamine if response is still inadequate; (d) it is appropriate to hold ALP and start oral corticosteroids (OCS) if rash affects > 30% body surface area and is recurrent or has moderate/severe symptoms; (e) if angioedema is present, it is appropriate to either hold ALP and start OCS, or permanently discontinue ALP tx. Conclusions: Until further evidence is available, these expert recommendations provide guidance on prevention and management of HG and rash related to ALP tx in routine clinical practice.

382 Background: Oral targeted therapies (OTTs) inhibiting CDK4/6, PI3K, and mTOR have established roles across multiple lines of therapy in patients with advanced hormone receptor–positive, HER2-negative breast cancer (HR+ BC). Abemaciclib, a CDK4/6 inhibitor (i), now also is approved in the adjuvant setting for eligible patients with early-stage HR+ BC. These OTTs are associated with various adverse events (AEs), such as cytopenias, diarrhea, hepatotoxicity, and rash. Optimal AE management is critical to promote patient adherence and achieve the best possible outcomes. Here we report an analysis of healthcare professional (HCP) management of AEs associated with OTTs in HR+ BC using an online decision support tool. Methods: The online tool was developed with 5 BC experts providing recommendations on the management of AEs associated with OTTs. Within the online tool, HCPs were prompted to input relevant patient case details through a series of predefined questions, including which OTT and type of AE the patient is experiencing, along with their management approach. Participants were then shown an expert recommendation based on the specific characteristics of that case and were asked if their management plan changed based on that recommendation. Results: Between September 2021 and April 2022, 557 cases were entered by 390 participants. Among 291 cases of patients currently receiving oral therapy, CDK4/6i therapy was most commonly selected (82%), followed by PI3Ki (11%) and mTORi (8%) therapy. The most common AE reported for CDK4/6i, PI3Ki, and mTORi therapy were cytopenias (56%), hyperglycemia (64%), and stomatitis (57%), respectively. With CDK4/6i, HCPs were discordant with expert recommendations for management of AEs reported in 44%, 39%, and 35% of entered cases with ribociclib, abemaciclib, and palbociclib, respectively. The greatest variance between HCP and expert recommendations were with management of VTE, hepatotoxicity, QT prolongation, and rash (Table). Among HCPs with discordant results from the experts, 50% changed their AE management plan after viewing the expert recommendation. Conclusions: These data suggest that HCPs may be challenged to optimally manage AEs related to OTTs in patients with HR+ BC. Use of an online tool may enhance HCP management of these AEs for patients with HR+ BC. A detailed analysis of the tool, including HCP planned management vs expert recommendations, will be presented.[Table: see text]

The cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) have become the standard of care, in combination with antiestrogen therapy, for patients with hormone receptor–positive (HR+)/HER2− advanced breast cancer. Various preclinical and translational research efforts have begun to shed light on the genomic and molecular landscape of resistance to these agents. Drivers of resistance to CDK4/6i therapy can be broadly subdivided into alterations impacting cell-cycle mediators and activation of oncogenic signal transduction pathways. The resistance drivers with the best translational evidence supporting their putative role have been identified via next-generation sequencing of resistant tumor biopsies in the clinic and validated in laboratory models of HR+ breast cancer. Despite the diverse landscape of resistance, several common, therapeutically actionable resistance nodes have been identified, including the mitotic spindle regulator Aurora Kinase A, as well as the AKT and MAPK signaling pathways. Based upon these insights, precision-guided therapeutic strategies are under active clinical development. This review will highlight the emerging evidence, in the clinic and in the laboratory, implicating this diverse spectrum of molecular resistance drivers.

This study evaluated neoadjuvant niraparib antitumor activity and safety in patients with localized HER2-negative, BRCA-mutated breast cancer. Twenty-one patients received niraparib 200 mg once daily in 28-day cycles. After 2 cycles, tumor response (≥30% reduction from baseline) by MRI was 90.5% and 40.0% (6/15) of patients who only received niraparib (2–6 cycles) had pathological complete response. No new safety signals were identified and high niraparib intratumoral concentration was observed.

Background Signaling through the cyclin-dependent kinase 4 and 6 (CDK4/6) pathway can mediate therapeutic resistance in HER2-positive breast cancer. Preclinical studies have demonstrated that CDK4/6 inhibitors can resensitize resistant HER2-positive breast cancer to anti-HER2 therapies. Patients and Methods We conducted a phase 1b/2 study of ribociclib (400 mg per day on a continuous schedule) plus trastuzumab (6 mg/kg every 3 weeks) in patients with advanced HER2-positive breast cancer previously treated with trastuzumab, pertuzumab, and trastuzumab emtansine. There were no restrictions on the number of prior therapy lines. Primary objective was clinical benefit rate at 24 weeks, and secondary objectives included safety, objective response, rate and progression-free survival. The study was enrolled at ClinicalTrials.gov as NCT02657343 . Results From March 2016 to March 2017, 13 patients were enrolled. One patient was found to have HER2-negative disease and did not receive treatment. Median number of prior lines in the metastatic setting was 5 (range, 0-14); 67% had hormone receptor–positive disease. No dose-limiting toxicities were observed during the safety run-in phase, and ribociclib was thus dosed at 400 mg per day continuously for the expansion cohort. Grade 3 adverse events were observed in 4 patients (33.3%) and included neutropenia (n = 2) as well as fatigue and pain in 1 patient each. No grade 4/5 adverse events or QTc prolongation were observed. One patient (8.3%) experienced stable disease > 24 weeks; no objective responses were observed, and median progression-free survival was 1.33 months (95% confidence interval, 0.92-2.57). Conclusion Continuous low-dose ribociclib (400 mg) plus trastuzumab is safe, with no new safety concerns. The limited activity observed in this study suggests that further study of CDK4/6 inhibitor/anti-HER2 combinations should focus on a less pretreated population.

Plasma genotyping identifies potentially actionable mutations at variable mutant allele frequencies, often admixed with multiple subclonal variants, highlighting the need for their clinical and functional validation. We prospectively monitored plasma genotypes in 143 women with endocrine-resistant metastatic breast cancer (MBC), identifying multiple novel mutations including HER2 mutations (8.4%), albeit at different frequencies highlighting clinical heterogeneity. To evaluate functional significance, we established ex vivo culture from circulating tumor cells (CTCs) from a patient with HER2-mutant MBC, which revealed resistance to multiple targeted therapies including endocrine and CDK 4/6 inhibitors, but high sensitivity to neratinib (IC50: 0.018 μM). Immunoblotting analysis of the HER2-mutant CTC culture line revealed high levels of HER2 expression at baseline were suppressed by neratinib, which also abrogated downstream signaling, highlighting oncogenic dependency with HER2 mutation. Furthermore, treatment of an index patient with HER2-mutant MBC with the irreversible HER2 inhibitor neratinib resulted in significant clinical response, with complete molecular resolution of two distinct clonal HER2 mutations, with persistence of other passenger subclones, confirming HER2 alteration as a driver mutation. Thus, driver HER2 mutant alleles that emerge during blood-based monitoring of endocrine-resistant MBC confer novel therapeutic vulnerability, and ex vivo expansion of viable CTCs from the blood circulation may broadly complement plasma-based mutational analysis in MBC.

Introduction: Despite the success of anti-HER2 therapy, acquired resistance usually develops in the metastatic setting. CDK4/6 pathway activity has been identified as a mediator of this resistance, and in preclinical studies the combination of CDK4/6 and HER2 blockade can be more effective than either therapy alone. We conducted a single-arm phase 1b/2 study of the CDK4/6 inhibitor ribociclib given with trastuzumab or T-DM1 to subjects with advanced, treatment-refractory HER2-positive breast cancer. The results of the trastuzumab cohort are presented below. The primary objective was to determine the clinical benefit rate (CBR) at 24 weeks, and secondary endpoints included objective response rate (ORR), progression-free survival (PFS), and adverse events. Methods: Individuals with locally advanced or metastatic, measurable HER2-positive breast cancer were eligible. All subjects must have previously received trastuzumab, pertuzumab, and T-DM1 as (neo)adjuvant or metastatic therapy. There was no limit on the number of prior lines of treatment. Patients with previous CDK4/6 inhibitor exposure, QTcF > 450msec on EKG, or without stable brain metastases were excluded. An initial safety run-in phase (with dose-limiting toxicity (DLT) monitoring) included six subjects who received trastuzumab (8mg/kg loading then 6mg/kg IV three-weekly) and ribociclib 400mg PO daily on a continuous schedule (cycle length 21 days). The study had a two-stage design. The first stage required 20 patients, at least 6 of whom must have demonstrated clinical benefit (CR+PR+ SD>24 weeks) in order to recruit 15 more patients to the second stage. All patients with accessible disease underwent metastatic tumor biopsies at baseline and C2D1. Results: 13 patients were enrolled (6 in the safety run-in and 7 in the expansion cohort). One patient was found to have HER2-negative disease and did not receive treatment. Patient characteristics are shown in Table 1 No DLTs were observed during the safety run-in phase, and ribociclib was thus used at 400mg po daily for the expansion cohort. Grade 3/4 toxicities were observed in 5 patients (41.7%) and included neutropenia (n=2), and fatigue, pain, and muscle weakness (all n=1). No patient demonstrated QTc prolongation >480 msec, or grade 3/4 LFTs. 1/12 patients ((8.3%); 95% CI 0.2%-38.5%) achieved stable disease>24 weeks; no objective responses were observed, and median PFS was 41.5 days. The trastuzumab portion of study was closed early due to limited clinical activity observed (the T-DM1 with ribociclib cohort remains open). Table 1Age (median, range)50.5 (42 - 71)Number of prior lines of systemic therapy for metastatic disease (median, range)5.5 (0-14)Number with Hormone receptor-positive disease (%)8 (67 %)Number of metastatic sites (median, range)2.5 (2 - 5) Conclusions: The combination of trastuzumab and ribociclib (400mg daily continuous schedule) is safe, with no new safety signals observed. The limited activity seen in this heavily pretreated population suggests that future efforts to incorporate CDK4/6 inhibition should be limited to a less extensively treat population. Citation Format: Goel S, Spring L, Rees R, Andrews C, Tahara RK, Mayer EL, Bardia A, Winer EP, Tolaney SM. A phase 1b/2 study of ribociclib plus trastuzumab for the treatment of advanced, treatment-refractory HER2-positive breast cancer [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P6-18-10.

Background: The addition of pertuzumab to trastuzumab and chemotherapy significantly improves the pathologic complete response (pCR) rate in HER2+ localized breast cancer in the preoperative setting. Although many patients are converted to breast conserving therapy (BCT) candidates by neoadjuvant HER2-directed therapy, a significant proportion opt for a mastectomy for various reasons. Among mastectomy procedures, nipple sparing mastectomy (NSM) is frequently chosen instead of non-nipple sparing mastectomy (NNSM). In this study, we evaluated the surgical and long-term outcomes of HER2+ patients receiving neoadjuvant pertuzumab-containing regimens. Methods: We performed a retrospective review of localized breast cancer patients treated with neoadjuvant pertuzumab-containing regimens from 2011 to 2016, who underwent BCT or mastectomy at an academic institution and two community-based practices. Disease characteristics, treatment regimens, surgical outcomes, and recurrence data were extracted from the electronic medical records. Results: Among 90 patients with stage II-III HER2+ breast cancer, 45 received AC-THP (50.0%), 26 received THP (with adjuvant AC) (29.0%), and 19 received TCHP (21.0%). The majority of patients had grade 3 tumors (61.1%), clinical stage II disease (80.0%), invasive ductal carcinoma (86.7%), and ER+ disease (65.6%). Thirty-seven (41.0%) patients underwent BCT and 53 (59.0%) patients underwent mastectomy. Among the mastectomy patients, 38 (71.7%) patients underwent bilateral mastectomies, specifically 33 (62.0%) patients underwent a NSM and 20 (38.0%) patients underwent a NNSM. The type of surgery that patients underwent stratified by type of neoadjuvant regimen is outlined in the Table 1 below. Most patients who underwent BCT and mastectomy received radiation, including 36 (97.3%) BCT, 24 (72.7%) NSM, and 18 (95.0%) NNSM. Over a median follow-up period of 33 months, 6 patients (6.7%) had recurrences with 2 (2.2%) local recurrences and 4 (4.4%) distant recurrences. The 2 local recurrences occurred in one patient who underwent BCT and one patient who underwent NNSM followed by post-mastectomy radiation. Conclusions: Among mastectomy patients, NSM was more commonly pursued than NNSM. Rates of local recurrence following pertuzumab-containing regimens for HER2-positive localized breast cancer were low overall, regardless of the type of surgery. Data on plastic surgery approaches and complication rates will be presented at the meeting. Table 1.Type of surgery in patients receiving neoadjuvant HER2-directed therapy. AC-THP (N = 45)TCHP (N = 19)THP (N = 26)BCT46.7%47.4%26.9%NNSM26.7%10.5%23.1%NSM26.7%42.1%50.0% Citation Format: Haddad SA, Spring LM, Jimenez RB, Vidula N, Comander A, Shin JA, Coopey SB, Gadd MA, Hughes KS, Taghian A, Smith BL, Isakoff SJ, Moy B, Bardia A, Specht MC. Surgical and long-term outcomes of patients receiving neoadjuvant pertuzumab-containing regimens for HER2-positive localized breast cancer [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P2-14-19.

This abstract was withdrawn by the authors. Citation Format: Metzger Filho O, Janiszewska M, Guo H, Yardley D, Mayer I, Spring L, Arteaga C, Wrabel E, DeMeo M, Freedman R, Tolaney S, Waks A, Bardia A, Parsons H, Partridge A, Mayer E, King T, Polyak K, Viale G, Winer E, Krop I. Withdrawn [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P1-15-01.

Background: The availability of multiple therapies has transformed the landscape of MBC, but also brought the challenge of selecting the right therapy for an individual patient. Furthermore, in patients with Hormone Receptor positive (HR+) breast cancer who have bone metastases only it may be difficult to assess effectiveness of therapy via imaging. Peripheral ctDNA detection and analysis by next-generation sequencing (NGS) has gained popularity in cancer diagnosis and therapeutics due to its relative noninvasiveness, ease of use, and high sensitivity. Here, we explore the utility of ctDNA change as a predictor for disease progression in MBC. We hypothesized that genomic progression is a harbinger of subsequent radiologic progression in patients with MBC. Methods: We analyzed change from pre-treatment (baseline) to on-treatment ctDNA mutant allele fraction (MAF) among patients with MBC. Patients receiving standard-of-care therapies or investigational agents on clinical trials at our institution were included. All patients were followed from the date of baseline test until death or data cutoff (6/20/2018). All peripheral blood specimens were collected and analyzed between 1/7/2016 and 3/1/2018 via NGS (Guardant360®). Peripheral blood specimens were sequenced prior to initiation of a new therapeutic regimen (baseline) and subsequently at least once while on-treatment, on average 4-12 weeks later. All patients had a follow-up CT scan of chest, abdomen and pelvis 2-4 weeks after the on-treatment NGS. A priori, we defined genomic progression as increase in ctDNA total MAF of at least 20% from baseline. We utilized Cox regression analysis to identify whether genomic progression was a predictor of radiologic progression, adjusting for common prognostic variables. Results: All patients (N= 77) were female, predominantly White (83.1%), and median age was 57 (range 32 to 77). Fifty one out of 77 patients (66.2%) were ER+, 5 HER2+, and 9 had triple negative breast cancer. The median MAF at baseline was 2.2% (range 0% - 61.7%). Common genomic alterations in ctDNA included PIK3CA, TP53, ESR1, AKT1, NF1. 27 out of 77 (35%) patients showed disease progression on the first subsequent CT scan, while 59 out of 77 (76.6%) progressed during the follow up time. We found that an increase in ctDNA MAF of at least 20% was a strong predictor of disease progression (HR =2.46, CI [1.14-5.32], p=0.02), compared to those who had a MAF increase of less than 20% or a decrease in total MAF. In multi-variable analysis, adjusting for age, number of prior therapies, type of therapy, and visceral metastases, increase in ctDNA remained a significant predictor for subsequent disease progression (HR =3.84, CI [1.63-9.07], p=0.002). Subset results in patients with bone metastases only, and relative comparison of ctDNA with standard tumor markers will be presented at the meeting. Conclusions: Genomic progression, identified by an increase in ctDNA MAF, is potentially an early predictor of subsequent disease progression in patients with MBC. Further research is needed to prospectively evaluate the clinical utility of ctDNA change as a surrogate marker in guiding treatment decision-making for patients with MBC. Citation Format: Velimirovic M, Juric D, Niemierko A, Spring LM, Vidula N, Malvarosa G, Yuen M, Moy B, Isakoff SJ, Ellisen LW, Bardia A. Genomic progression, detected by circulating tumor DNA (ctDNA) sequencing, as an early predictor of disease progression in metastatic breast cancer (MBC) [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P4-08-08.

Introduction: The advent of cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) has transformed the clinical practice of HR+/HER2- metastatic breast cancer. Palbociclib, ribociclib, and abemaciclib have been approved in conjunction with anti-estrogens, while abemaciclib has also been approved as monotherapy based on single agent activity in the MONARCH-1 trial (objective response rate/ORR: 19.7% and median progression-free-survival/PFS = 6.0 months; Dickler M et al CCR 2017). However, there is limited insight into the mechanisms governing resistance to CDK 4/6i and the potential utility of continued CDK4/6i after progression on a prior CDK 4/6i-based therapy. Methods: We evaluated the clinical outcomes of patients with metastatic HR+/HER2- breast cancer who had received abemaciclib following an initial course of palbociclib-based therapy at our institution. In addition, we conducted genomic analysis utilizing next-generation sequencing of tissue samples and blood (cell-free DNA/cfDNA analysis) where available. Results: From June, 2014 through July, 2018, a total of 49 patients received abemaciclib, and 14 patients had prior palbociclib exposure. One patient was deceased shortly after initiating abemaciclib and one patient was lost to follow-up. Among the 12 remaining patients, eight had sequential courses of CDK4/6-based therapy, while four patients had at least one intervening non-CDK 4/6i based regimen. At data-cutoff of 8/15/2018, five patients (41.7%) had early progression on abemaciclib (PFS equal to or less than 120 days) while three (25%) patients had ongoing benefit (PFS greater than 120 days, two of three actively on therapy). Three additional patients had recently initiated abemaciclib therapy (less than 120 days prior to current analysis). Preliminary analysis of baseline cfDNA results in patients with early progression on abemaciclib therapy after prior CDK4/6i revealed the presence of RB1 mutation, FGFR1 amplification, and TP53 mutation, among others. Additional analyses with mature clinical data (including updated PFS and ORR), toxicity assessment during secondary CDK4/6i exposure, and further analysis of genomic sequencing results will be provided at the meeting. Conclusions: The majority of patients had early disease progression on abemaciclib after prior exposure to CDK4/6i suggesting potential cross-resistance to CDK4/6i mediated by common drivers. However, a subset of patients derived clinical benefit with continued exposure to CDK4/6i, highlighting the need for additional research to evaluate potential predictive biomarkers and guide rational utilization of continued CDK4/6 blockade in metastatic HR+/HER2- breast cancer. Citation Format: Wander SA, Spring LM, Stein CR, Yuen M, Zangardi M, O'Shaughnessy J, Bardia A. Abemaciclib after prior palbociclib exposure in patients with metastatic hormone-receptor positive (HR+)/HER2- breast cancer [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P6-18-39.

Fewer than 1% of all breast cancers occur in men. As a result, a distinct lack of data exists regarding the management and outcomes in this cohort. Any male patient with pathologically confirmed breast cancer diagnosed between August 2000 and October 2017 at either Massachusetts General Hospital or Brigham and Women’s Hospital/Dana-Farber Cancer Institute and their affiliate satellite locations were included. Primary chart review was used to assess clinical and pathologic characteristics. Patient and treatment variables were reported via descriptive statistics. Local–regional failure (LRF), overall survival (OS), breast cancer-specific survival (BCSS), and disease-free survival (DFS) were estimated using the Kaplan–Meier method. 100 patients were included in this study. Median follow-up was 112 months (range 1–220 months). Approximately 1/3 of patients experienced at least a 3-month delay to presentation. 83 patients ultimately underwent mastectomy as definitive surgical treatment. 46 patients received adjuvant radiation therapy, and 37 patients received chemotherapy. Of 82 hormone receptor-positive patients with invasive cancer, 94% (n = 77) received endocrine therapy. Of the fifty-eight patients who underwent genetic testing, 15 (26%) tested positive. The 5-year OS, BCSS, DFS, and LRF rates were 91.5%, 96.2%, 86%, and 4.8%, respectively. Delay to presentation was not associated with worse survival. Male breast cancer remains a rare diagnosis. Despite this, the majority of patients in this study received standard of care therapy and experienced excellent oncologic outcomes. Penetration for genetic testing improved over time.

The receptor-based classification of breast cancer predicts its optimal therapy. Hormone Receptor (HR) positive breast cancer is treated with endocrine therapy, and HER2+ disease is treated with HER2-targeted therapy. Triple negative breast cancer (TNBC), defined as tumors lacking HR and HER2, represents an aggressive subtype of breast cancer associated with poor prognosis. Development of targeted therapy for this subtype has been challenging since TNBC usually lacks targetable genomic alterations. However, the advent of antibody drug conjugates (ADC) to target antigens overexpressed in breast cancer has opened the door to a new class of breast cancer therapeutics. In this review, we describe the current FDA-approved ADC therapies for breast cancer, including sacituzumab govitecan, as well as agents currently in advanced stages of investigation. In addition, we review the potential therapeutic application of ADCs across different breast cancer subtypes. In the future, therapeutic advances in ADCs targeting different antigens could redefine the current receptor-based classification of breast cancer.

Combining cyclin-dependent kinase (CDK) inhibitors with endocrine therapy improves outcomes for metastatic estrogen receptor positive (ER+), HER2 negative, breast cancer patients. However, the value of this combination in potentially curable earlier stage patients is not clear. Using single cell transcriptomic profiling, we examined the evolutionary trajectories of early stage breast cancer tumors using serial tumor biopsies from a clinical trial of preoperative endocrine therapy (letrozole) alone or in combination with the cell cycle inhibitor ribociclib. Applying hierarchical regression and Gaussian process mathematical modelling, we classified each tumor by whether it shrinks or persists with therapy and determined cancer phenotypes related to evolution of resistance and cell cycle transcriptional rewiring. We found that all patients’ tumors undergo subclonal evolution during therapy, irrespective of the clinical response. However, tumors subjected to endocrine therapy alone showed reduced diversity over time, while those facing combination therapy exhibited increased diversity. Despite different subclonal diversity, single nuclei RNA sequencing uncovered common phenotypic changes in tumor cells that persist following treatment. In these tumors, cancer cells with accelerated loss of estrogen signaling have convergent up-regulation of the JNK pathway, while cells that maintain estrogen signaling during therapy show potentiation of CDK4/6 activation consistent with ERBB4 and ERK signaling up-regulation. These convergent phenotypes were associated with growing tumors resistant to combination therapy. Cell cycle reconstruction identified that these tumors can rebound during combination therapy treatment, indicating stronger selection and promotion of a proliferative state. These results indicate that combination therapy in early stage ER+ breast cancers with ER and CDK inhibition drives rapid evolution of resistance via a shift from estrogen signaling to alternative growth factor receptor mediated proliferation and JNK signaling activation, concordant with a bypass in the G1 checkpoint.