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XLSX file - 23K, Mapping statistics for genome sequencing of tumor and germline DNA from mTNBC

Supplementary Figure S3: Molecular characterisation of the MC6 subtype in six TNBC cohorts.

Supplementary Table S16: Results from the gene set enrichment analysis of 28 different immune signatures across the METABRIC-set 15 (MC subtypes) classification. Supplementary Table S17: Table representing the copy number status of the five genes part of the MAPK inactivation score across the METABRIC-set 15 (MC subtypes) classification. Supplementary Table S18: Output of the multivariable logistic regression analysis for the MC6 and the BL1 subtype in Sanofi Phase II. Supplementary Table S19: Output of the multivariable logistic regression analysis for the MC6 and the BL1 subtype in Sanofi Phase III. Supplementary Table S20: Results from the drug screen performed between MC6 and non-MC6 TNBC cell lines.

The identification of early breast cancer patients who may benefit from adjuvant chemotherapy has evolved to include assessment of clinicopathologic features such as tumor size and nodal status, as well as several gene-expression profiles for ER-positive, HER2-negative cancers. However, these tools do not reliably identify patients at the greatest risk of recurrence. The mutation and copy-number landscape of triple-negative breast cancer (TNBC) subtypes defined by gene expression is also largely unknown, and elucidation of this landscape may shed light on novel therapeutic opportunities. The USO01062 phase III clinical trial of standard chemotherapy (with or without capecitabine) enrolled a cohort of putatively high-risk patients based on clinical features, yet only observed a 5-year disease-free survival event rate of 11.6%. In order to uncover genomic aberrations associated with recurrence, a targeted next-generation sequencing panel was used to compare tumor specimens from patients who had a recurrence event with a matched set who did not. The somatic mutation and copy-number alteration landscapes of high-risk early breast cancer patients were characterized and alterations associated with relapse were identified. Tumor mutational burden was evaluated but was not prognostic in this study, nor did it correlate with PDL1 or CD8 gene expression. However, TNBC subtypes had substantial genomic heterogeneity with a distinct pattern of genomic alterations and putative underlying driver mutations.Implications:The present study uncovers a compendium of genomic alterations with utility to more precisely identify high-risk patients for adjuvant trials of novel therapeutic agents.

Supplementary Information: Extended methods.

Supplemental Methods describing NGS and gene expression studies.

XLSX file - 45K, Genes containing breakpoint from translocation in mTNBC

The molecular complexity of triple-negative breast cancers (TNBCs) provides a challenge for patient management. We set out to characterize this heterogeneous disease by combining transcriptomics and genomics data, with the aim of revealing convergent pathway dependencies with the potential for treatment intervention. A Bayesian algorithm was used to integrate molecular profiles in two TNBC cohorts, followed by validation using five independent cohorts (n = 1,168), including three clinical trials. A four-gene decision tree signature was identified, which robustly classified TNBCs into six subtypes. All four genes in the signature (EXO1, TP53BP2, FOXM1, and RSU1) are associated with either genomic instability, malignant growth, or treatment response. One of the six subtypes, MC6, encompassed the largest proportion of tumors (∼50%) in early diagnosed TNBCs. In TNBC patients with metastatic disease, the MC6 proportion was reduced to 25%, and was independently associated with a higher response rate to platinum-based chemotherapy. In TNBC cell line data, platinum sensitivity was recapitulated, and a sensitivity to the inhibition of the phosphatase PPM1D was revealed. Molecularly, MC6-TNBCs displayed high levels of telomeric allelic imbalances, enrichment of CD4+ and CD8+ immune signatures, and reduced expression of genes negatively regulating the MAPK signaling pathway. These observations suggest that our integrative classification approach may identify TNBC patients with discernible and theoretically pharmacologically tractable features that merit further studies in prospective trials.

XLSX file - 273K, Somatic genic focal copy number changes in mTNBC

XLSX file - 598K, edgeR differential expression results in mTNBC for select cancer related genes

XLSX file - 607K, Outlier differential expression results in mTNBC for select cancer related genes

FoundationOne sequencing data for n=399 breast cancer population. Each sheet contains a distinct type of alteration. The clinical covariates used in our analysis are included.

XLSX file - 61K, List of somatic point mutations in mTNBC detected by NGS sequencing analysis

Enriched Pathway Analysis.

XLSX file - 42K, Ingenuity Canonical Pathways results for mTNBC based on edgeR differential expression results

XLSX file - 40K, Characteristics of mTNBC study population

Supplemental figures 1,2,4-8 as supporting figures to the manuscript.

PDF file - 1635K, PET/CT images of mTNBC2 breast lesion before and after treatment on combination MEK and AKT inhibitors

XLSX file - 48K, Transcriptome sequencing (RNA-seq) run statistics for mTNBC

PDF file - 135K, Validation of RB1 39bp homozygous deletion in mTNBC1

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

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

AKT S473 distribution based on ER expression measured by IHC for 31 lesions included of the discovery set. ER was measured in a binary scale (Panel A) and in continuous scale using the H-Score (Panel B).

Purpose: Little is known about the molecular signatures associated with specific metastatic sites in breast cancer. Using comprehensive multi-omic molecular profiling, we assessed whether alterations or activation of the PI3K–AKT–mTOR pathway is associated with specific sites of breast cancer metastasis.Experimental Design: Next-generation sequencing–based whole-exome sequencing was coupled with reverse-phase protein microarray (RPPA) functional signaling network analysis to explore the PI3K–AKT–mTOR axis in 32 pretreated breast cancer metastases. RPPA-based signaling data were further validated in an independent cohort of 154 metastatic lesions from breast cancer and 101 unmatched primary breast tumors. The proportion of cases with PI3K–AKT–mTOR genomic alterations or signaling network activation were compared between hepatic and nonhepatic lesions.Results: PIK3CA mutation and activation of AKT (S473) and p70S6K (T389) were detected more frequently among liver metastases than nonhepatic lesions (P < 0.01, P = 0.056, and P = 0.053, respectively). However, PIK3CA mutations alone were insufficient in predicting protein activation (P = 0.32 and P = 0.19 for activated AKT and p70S6K, respectively). RPPA analysis of an independent cohort of 154 tumors confirmed the relationship between pathway activation and hepatic metastasis [AKT (S473), mTOR (S2448), and 4EBP1 (S65); P < 0.01, P = 0.02, and P = 0.01, respectively]. Similar results were also seen between liver metastases and primary breast tumors [AKT (S473) P < 0.01, mTOR (S2448) P < 0.01, 4EBP1 (S65) P = 0.01]. This signature was lost when primary tumors were compared with all metastatic sites combined.Conclusions: Breast cancer patients with liver metastasis may represent a molecularly homogenized cohort with increased incidence of PIK3CA mutations and activation of the PI3K–AKT–mTOR signaling network. Clin Cancer Res; 23(16); 4919–28. ©2017 AACR.

Supplementary material legend

Concordance between PIK3CA, AKT, and PTEN mutation status and AKT (S473) and p70S6 (T389) activation.

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

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

Treatment (tx) choices for HER2+ early stage breast cancer (EBC) have become increasingly complex. Clinicians and patients must decide 1) which chemotherapy and HER2-targeted agents to use, 2) the sequence of surgery and chemotherapy: either neoadjuvant (neoadj) or adjuvant (adj) tx, and 3) whether to shorten or extend maintenance HER2-targeted tx. As tx options expand, so does the need for online decision aids. One online decision support tool was developed in 2015 to provide specific tx recommendations for pts with EBC and showed that community healthcare providers (HCPs) did not consistently align with experts for neoadj or adj tx of many pts with EBC (SABCS 2015 Abs P5-09-04). This study includes analysis of neoadj and adj tx practice patterns of 5 breast cancer experts based on their tx recommendations for 270 unique HER2+ EBC case scenarios made for development of a 2018 online decision tool. We aim to compare these recommendations with the intended treatment of clinicians using the tool. Results Experts agree on neoadj tx approaches: initial surgery, no neoadj tx for pts with cT1a/b N0 tumors; neoadj tx before surgery for pts with ≥cT2 or N+ tumors. There was disparity among experts for pts with cT1c N0 disease: 3 experts recommend neoadj TCH±P and 2 recommend proceeding directly to surgery. Experts generally recommend adj TCHP for pts with stage II N+ or higher HER2+ EBC who did not receive neoadj tx. In addition, 5/5 experts would consider extended adj tx with neratinib for these pts if HR+ and 2/5 experts would also consider neratinib if HR–. In pts who received neoadj chemo+HER2 tx, post-surgery management depends on response to neoadj tx. For pts with pCR, 5/5 experts generally agree on continuing H+P if both were given as neoadj tx or H alone if only H given as neoadj tx for a total of 1 yr of anti-HER2 Ab tx and 2/5 experts would consider extended adj tx with neratinib for HR+ disease. For pts with residual disease, experts would recommend continuing H+P if both were given as neoadj tx and most would add P for subsequent adj tx if H alone was given to complete a total of 1 yr of anti-HER2 Ab tx (Table1). All experts would consider extended adj tx with neratinib for HR+ disease and 3/5 experts would also consider neratinib for HR– disease. None of the experts recommended less than 12 mos of adj HER2-targeted tx. We will present analyses of cases entered into our online tool and detailed comparisons of expert and the intended treatment of clinicians using the tool. Conclusions Practice patterns are changing rapidly and are more complex in response to the evolving treatment landscape for HER2+ EBC. This analysis highlights several areas of expert consensus; however, disparities remain for select cases. The current tool addresses an unmet medical need for expert-led evaluation of HER2+ EBC tx choices and warrants further investigation. Expert Recommendations: Initial Adj HER2 Ab Tx After Neodj Tx With H Alone ExpertsResponse12345pCR (HR-)HHHHHpCR (HR+)HHHHHypT1a-c N0 (HR-)H + PHH + PH + PH + PypT1a-c N0 (HR+)H + PHHH + PHypT2 N0 (HR-)H + PH + PH + PH + PH + PypT2 N0 (HR+)H + PH + PHH + PH + PypTany N+ (HR+ or HR-)H + PH + PH + PH + PH + P Citation Format: Holmes FA, Rosenthal KM, Hurvitz S, Pegram MD, Yardley DA, Obholz KL, O'Shaughnessy J. Consensus and disagreement among experts for treatment of patients with HER2+ early-stage breast cancer suggests unmet need for online decision support tool [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P6-17-36.

Background: Ribociclib (ribo) + letrozole (LET) demonstrated efficacy and safety in first-line treatment of patients (pts) with hormone receptor–positive (HR+), HER2− advanced breast cancer (ABC). Most endocrine therapy (ET)–naive pts with de novo ABC respond to ET, but first-line monotherapy with ET or fulvestrant elicited only moderate efficacy in the FALCON study of pts with visceral metastases (mets). Visceral mets are associated with poor prognosis and may warrant novel treatment options in addition to ET. Here, we present clinical outcomes of treatment with ribo in pts with de novo ABC and visceral mets. Methods: In the MONALEESA-2 study, postmenopausal women with HR+, HER2− ABC (N=668) were randomized (1:1) to receive either ribo 600 mg/d or placebo (3 wk on/1 wk off) + LET 2.5 mg/d (continuous). The primary endpoint was median progression-free survival (mPFS). Results: All pts in this analysis (n=227) had de novo ABC; 108 pts had visceral mets (ribo, n=53; placebo, n=55). Baseline characteristics were similar between the ribo and placebo groups. The median follow-up time was 26.4 months. In pts with visceral mets, mPFS was significantly higher in the ribo group (30.3 months) than in the placebo group (14.1 months; hazard ratio, 0.52; 95% CI, 0.295–0.905; P=0.019). Rates of PFS in these pts in the ribo vs placebo group, respectively, were 76% vs 60% at 12 months and 60% vs 36% at 24 months. Among the pts with visceral mets, clinical benefit rate (CBR) was 79% vs 71% in the ribo vs placebo group, and overall response rate (ORR) in pts with measurable disease at baseline was 55% vs 46%, respectively. In pts without visceral mets (ribo, n=61; placebo, n=58), PFS rates in the ribo vs placebo group, respectively, were 87% vs 72% at 12 months and 66% vs 51% at 24 months. Safety results were consistent with the overall population, and responses were durable with ribo + LET irrespective of whether the pts had visceral or nonvisceral mets. Conclusions: Clinical outcomes from this analysis of the MONALEESA-2 study are consistent with those of the overall population, and ribo + LET prolonged the mPFS and improved ORR and CBR in pts with de novo ABC with visceral mets vs placebo + LET. Citation Format: O'Shaughnessy JA, Arteaga CL, Hart LL, Lindquist DL, Beck JT, Purkayastha DD, Caria N, Hortobagyi GN. Treatment benefit of ribociclib + letrozole in patients with de novo disease and visceral metastases from the MONALEESA-2 study [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 P6-18-01.

Background: In the Phase III MONALEESA (ML) trials, ribociclib (RIB; cyclin-dependent kinase 4/6 inhibitor) + endocrine therapy (ET) significantly improved progression-free survival (PFS) vs placebo (PBO) + ET in patients (pts) with hormone receptor-positive (HR+), HER2-negative (HER2–) advanced breast cancer (ABC). Here we report key patient-reported outcomes (PROs) for pts treated with RIB-based regimens of interest (i.e. with a non-steroidal aromatase inhibitor [NSAI] or fulvestrant [FUL]) in the ML-2, -3, and -7 trials. Methods: Postmenopausal pts with HR+, HER2– ABC and no prior ET for advanced disease received RIB (600 mg/day; 3-weeks-on/1-week-off) + letrozole (2.5 mg/day; ML-2 [NCT01958021]), or FUL (500 mg every 28 days, with an additional dose on Day 15 of Cycle [C] 1; ML-3 [no prior ET for ABC subgroup only; NCT02422615]). Premenopausal pts with no prior ET and ≤1 line of chemotherapy for advanced disease received RIB + NSAI (anastrozole [1 mg/day]/letrozole [2.5 mg/day]) + goserelin (3.6 mg every 28 days; ML-7 [NCT02278120]). The primary endpoint for all trials was PFS. PROs were a secondary endpoint of all trials and were evaluated using EORTC QLQ-C30, QLQ-BR23 (ML-2 and ML-7), EQ-5D-5L, WPAI-GH (ML-7 only), and BPI-SF (ML-3 only) questionnaires. Changes from baseline and time to 10% deterioration (TTD) in health-related quality of life (HRQoL) were analyzed using linear mixed-effect and stratified Cox regression models, respectively. Results: A total of 1530 pts were included in this analysis. Questionnaire compliance was high across trials (ML-2/ML-3: >90%; ML-7: >80%). On-treatment HRQoL (EORTC QLQ-C30 global health status/quality of life [QoL] score) was maintained from baseline up to C34, C28, and C17 in both treatment arms for ML-2, ML-3, and ML-7, respectively. In ML-7, mean overall HRQoL scores continued to improve in the RIB arm from C18 to C28, but scores decreased in the PBO arm. At end of treatment, mean overall HRQoL scores decreased in both arms across trials. Median TTD (RIB vs PBO) was similar between arms, favoring the RIB arms (ML-2: 27.7 vs 27.6 months; hazard ratio 0.944; 95% confidence interval [CI] 0.720–1.237; ML-3: not reached [NR] vs 22.4 months; hazard ratio 0.721; 95% CI 0.484–1.074; ML-7: 24.0 vs 19.4 months; hazard ratio 0.759; 95% CI 0.561–1.028). Clinically meaningful reductions in EORTC QLQ-C30 pain score (>5 points from baseline) were observed in the RIB arm of ML-2 from as early as C3 and were sustained vs only at C7 and C13 in the PBO arm. Clinically meaningful reductions in pain were observed from C22 to C28 in the RIB arm of ML-7 vs only at C28 in the PBO arm. In ML-3, clinically meaningful reductions in pain were observed from C3 to C5, C11–17, and at C22 and C28 in the RIB arm vs C17–C25 in the PBO arm. Furthermore, median TTD of the BPI-SF pain severity index score was NR in either arm of ML-3 (hazard ratio 0.858; 95% CI 0.554–1.330). Conclusions: In addition to significantly prolonging PFS, RIB consistently maintains QoL regardless of ET combination partner. RIB + ET is also associated with clinically meaningful reductions in pain vs PBO + ET across a broad population of pts with HR+, HER2– ABC. Citation Format: Beck JT, Neven P, Esteva FJ, Bardia A, Harbeck N, Hurvitz S, O'Shaughnessy J, Verma S, Lanoue B, Alam J, Kong O, Chandiwana D, Chia S. Patient-reported outcomes with ribociclib-based therapy in hormone receptor-positive, HER2-negative advanced breast cancer: results from the phase III MONALEESA-2, -3, and -7 trials [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 P6-18-14.

Background In MONARCH 1 (NCT02102490), abemaciclib demonstrated promising single-agent activity and tolerability in a population of heavily pretreated women with refractory HR+, HER2- metastatic breast cancer (MBC).1 Confirmed objective response rate (ORR) was 19.7% (95% CI: 13.3, 27.5) and at 18 months minimum follow-up median overall survival (OS) was 22.3 months. Due to the single-arm trial design of MONARCH 1, there is a need to view these results in clinical context relative to available treatment options. This study compared the OS results of abemaciclib in MONARCH 1 vs that in a real-world single-agent chemotherapy cohort with similar patient and disease characteristics. Methods MONARCH 1 study design and key eligibility criteria were previously described.1 The real-world cohort was based on Flatiron Health electronic health records-derived, nationally representative (USA-based) database comprising patient-level structured and unstructured data, curated via technology-enabled abstraction, for patients with MBC between January 1, 2011 through February 28, 2018. A real-world single-agent chemotherapy cohort was created based on the key eligibility criteria of MONARCH 1 and included patients diagnosed with HR+, HER2- MBC who received single-agent chemotherapy (eribulin, capecitabine, gemcitabine, or vinorelbine) following 1-2 prior chemotherapy regimens in the metastatic setting, had an ECOG PS of 0-1, and no prior CDK4 & 6 therapy. The index date was the start of the eligible single-agent chemotherapy, and patients were followed from the index date until date of death, loss to follow-up, or end of the database, whichever occurred earlier. OS results were adjusted using 2 methods (Mahalanobis distance matching and entropy balancing with bootstrapping) to account for baseline demographic and clinical differences between the real-world and trial cohorts. Results A real-world cohort (n=281) with eligibility criteria similar to the MONARCH 1 population (n=132) was identified. A subsequent matching based on Mahalanobis distance was performed to match MONARCH 1 population (n=108) with the real-world cohort (n=108). The matched cohorts demonstrated similar patient and disease characteristics. Median OS was 22.3 months in the abemaciclib arm vs 13.6 months in the matched cohort with an estimated hazard ratio (HR) of 0.54 (95% CI: 0.37, 0.77). Results of a sensitivity analysis performed using entropy balancing were consistent with an adjusted median OS of 12.7 months in the real-world cohort (n=281)with HR of 0.57 (95% CI from bootstrapping: 0.44, 0.78). Conclusion Methodological advances to adjust for potential biases, and improvements in data quality, have evolved enabling the ability to leverage a real-world cohort as an external comparator arm. This study demonstrates the ability to create a real-world chemotherapy cohort suitable to serve as a comparator for MONARCH 1. These exploratory results suggest a survival advantage and adequately place the clinical benefit of abemaciclib monotherapy in clinical context. References Dickler et al, CCR 2017 Citation Format: Rugo H, Dieras V, Cortes J, Patt D, Wildiers H, O'Shaughnessy J, Zamora E, Yardley DY, Carter GC, Sheffield KM, Li L, Andre VA, Derbyshire RE, Li XI, Frenzel M, Huang Y-J, Dickler MN, Tolaney SM. Real-world survival of heavily pretreated patients with refractory HR+, HER2- metastatic breast cancer receiving single-agent chemotherapy - A comparison with MONARCH 1 [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 P6-18-19.

Background: Sacituzumab govitecan is an antibody-drug conjugate consisting of SN-38, the active metabolite of irinotecan, conjugated to a humanized mAb targeting Trop-2 (trophoblastic antigen-2), which is highly expressed in many epithelial cancers. A phase I/II basket trial (NCT01631552) investigated its activity in patients (pts) with advanced epithelial cancers. Herein, we summarize pooled safety and efficacy findings in 162 pts with HER2-negative metastatic breast cancer (mBC) accrued between 7/2013 and 6/2017 who received at least 2 prior therapies for metastatic disease and were treated with sacituzumab govitecan at the 10 mg/kg dose level. Methods: Patients with triple-negative (N=108) and patients with hormone-receptor positive (N=54) mBC received 10 mg/kg sacituzumab govitecan on days 1 & 8 of a 21-day cycle continued until progression or unacceptable toxicity. All pts had measurable disease by CT or MRI. Efficacy was assessed locally by RECIST 1.1 including overall response rate (ORR) and Kaplan-Meier estimates of duration of response (DOR), progression-free survival (PFS) and overall survival (OS). Adverse events (AE) were evaluated according to CTCAE v4.0 Results: The patient cohort (161 female /1 male; median age 55 yrs, range 31-80) received a median of 4 prior therapies for metastatic disease (range 2-17), with prior chemotherapy agents in the metastatic setting including taxane (68%), capecitabine (60%), platinum (59%), gemcitabine (44%), eribulin (41%), and anthracycline (38%). 77 pts have died, with 57 in long-term follow-up and 28 still on treatment at data cutoff. The median number of administered sacituzumab govitecan doses was 14 (range 1-88). Treatment was generally well tolerated. 29% of pts had dose reductions, 3% discontinued treatment due to drug-related AEs, and there were no treatment-related deaths. Based on currently available AE data, grade ≥ 3 toxicity included neutropenia (43%), anemia (9.5%), diarrhea (7.0%) and febrile neutropenia (6.3%). For the TNBC subgroup, with a median follow-up of 9.3 months, the ORR was 33% (3 CRs + 33 PRs /108) with a median DOR of 8.3 months (95% CI: 4.8 – 11.6). For the ER+ subgroup, with a median follow-up of 10.0 months, the ORR was 31% (17 PRs/54) with a median DOR of 7.4 months (95% CI: 4.4 – 18.3). The combined HER2Neg ORR was 33% (3 CRs+50 PRs/162), with a median DOR of 8.3 months (95% CI: 4.9 - 10.8), PFS of 5.6 months (95% CI: 5.1 – 6.9) and OS of 13.0 months (95% CI: 11.5 - 15.0). The ORR was comparable for pts ≤ 50 yrs. old [32.2% (19/59)] vs. > 50 yrs old [33.0% (34/103)] and little different for pts with 2 prior therapies [35.4% (17/48)] vs. >2 prior therapies [31.6% (36/114)]. Conclusions: Monotherapy with sacituzumab govitecan was well tolerated with a manageable safety profile, and achieved a 30+% objective response rate among heavily pre-treated patients with HER2-negative metastatic breast cancer regardless of ER status. Citation Format: Kalinsky K, Isakoff SJ, Tolaney SM, Juric D, Mayer IA, Vahdat LT, Diamond JR, O'Shaughnessy J, Moroose RL, Santin AD, Shah NC, Abramson V, Goldenberg DM, Sharkey RM, Washkowitz SA, Wegener WA, Iannone R, Bardia A. Safety and efficacy of sacituzumab govitecan (anti-Trop-2-SN-38 antibody-drug conjugate) as ≥3rd-line therapeutic option for treatment-refractory HER2-negative metastatic breast cancer (HER2Neg 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 P2-11-01.

Breast cancer is the most common tumor type observed in women in the United States. The majority of patients are diagnosed at an early stage, but the disease often recurs after initial treatment. Human epidermal growth factor receptor 2 (HER2) gene amplification is present in approximately 20% to 25% of breast tumors and is associated with invasive disease and an aggressive phenotype. The addition of anti-HER2 therapy to chemotherapy has significantly improved the prognosis for patients with these aggressive tumors. However, despite the dramatic advances in survival achieved by targeting HER2, patients with these tumors are still at risk for recurrence after initial treatment. In an effort to address the risk for recurrence, recent clinical trials have evaluated the efficacy and safety of anti-HER2 antibodies and HER2 tyrosine kinase inhibitors as adjuvant or extended adjuvant therapy. Meaningful reductions have been observed in the risk for invasive and distant recurrence, particularly in certain HER2-positive breast cancer subpopulations. To optimize adjuvant treatment, therapies should be prescribed for patient subpopulations based on factors such as underlying risk profile, response to initial therapy, and patient preference. Neratinib is a small-molecule, irreversible tyrosine kinase inhibitor of HER1, HER2, and HER4 that penetrates the blood-brain barrier. This monograph examines neratinib in the setting of early-stage/extended adjuvant breast cancer, with a focus on clinical trial data, the mechanism of action, and ways to optimize clinical use.

Circulating tumor cells (CTCs), CTC heterogeneity and distinct morphological CTC subtypes predict worse survival in metastatic breast cancer (MBC)BackgroundThe presence of CTCs has been shown to be a poor prognostic factor in patients with MBC. Studies in prostate cancer have shown patients with distinct morphological subtypes of CTCs have worse outcomes than high CTC burden alone and could have treatment implications. In this study, we report a comprehensive analysis of CTC phenotypes in MBC and their impact on survival.MethodsA total of 148 blood samples from 90 patients with MBC whose disease was progressing on therapy were enrolled for CTC analysis. Blood was sent overnight to Epic Sciences, processed onto glass slides and biobanked. Replicate slides were stained with antibodies targeting the androgen receptor (AR), estrogen receptor (ER), and human epidermal growth factor receptor 2 (HER2) in addition to cytokeratin, CD45, and DAPI. Total CTCs were quantified per sample from approximately 3 mL of blood. A threshold defining positive AR, ER, and HER2 protein expression was set using cultured cancer cell lines expressing the individual proteins. CTC morphology subtypes (heterogeneity [Scher et al Cancer Res 2017], small cell/neuroendocrine-like [SC/NE; Brown et al CCR 2021] and chromosomal instability [CIN+; Schonhoft et al Cancer Res 2020]) were quantified as previously described. High heterogeneity samples (Het+) were defined as having a Shannon Index (SI; a measure of morphologic diversity) of ≥1. CIN positivity was defined as having ≥0.7 CIN+ CTC/mL. Association with these CTC subtypes and survival were evaluated with a univariate COX proportional hazard model. ResultsOver 90% of samples and patients had CTCs (Table 1). The percentage of patients with the CTC subtypes evaluated are below. Table 1. Percentage of blood samples with CTCs and CTC subtypes in MBC patients, by MBC subtype The presence of CTCs was associated with worse survival, with a median survival of 15.3 months (mos) vs 24.0 mos with no CTCs (p=0.028). The presence of AR+ or HER2+ CTCs was not associated with survival. Analysis of ER is ongoing and will be presented. High morphologic heterogeneity or the presence of the SC/NE or CIN+ CTC subtypes, predicted for a worse survival outcome (Table 2). Table 2. Overall survival of patients with and without distinct CTC subtypes CTC morphological subtypes did not correlate with each other, except CTC heterogeneity by SI which correlated weakly with SC/NE and CIN+. HER2+ CTCs strongly correlated with a higher SI while AR+ CTCs did not. AR and HER2 expression did not associate with the CIN+ or SC/NE subtypes. ConclusionsDigital pathology analysis of CTCs identifies distinct CTC morphological subtypes that predict for worse prognosis in MBC patients. To our knowledge, this is the first report of SC/NE CTCs in MBC patients and that MBC patients with SC/NE and CIN+ CTCs have worse outcomes. Longitudinal characterization of CTC subtypes across the MBC continuum could potentially identify effective therapies against these more lethal cancers. Citation Format: Joyce A O'Shaughnessy, Maren K Levin, Esther San Roman Rodriguez, James Lu, Joshua T Jones, Amanda KL Anderson, Alisa Tubbs, Joseph D Schonhoft, Rick Wenstrup. Circulating tumor cells (CTCs), CTC heterogeneity and distinct morphological CTC subtypes predict worse survival in metastatic breast cancer (MBC) [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 P2-02-03.

Background: Human epidermal growth factor receptor 2 (HER2) positivity in breast cancer portends an aggressive tumor behavior and poor prognosis and is associated with a positive response to trastuzumab treatment. Prior immunohistochemistry and RNA sequencing of breast tumor tissues suggest that trastuzumab may recruit and activate anti-tumor T cells. Tumor infiltrating lymphocytes have been associated with improved response in patients with HER2+ early breast cancer treated with neoadjuvant trastuzumab plus chemotherapy. However, these cells have not previously been characterized at the single cell level in tumor tissue or in the periphery. Assessing the T cell component in the peripheral blood via single-cell sequencing enables high sensitivity detection of rare cells, may identify T cell antigen receptors (TCR) involved in the anti-tumor response, and could lead to a non-invasive means of monitoring trastuzumab-mediated immune activity. Here we perform single cell sequencing of the blood T cell repertoire in breast cancer patients pre- and post-trastuzumab treatment. Methods: To characterize T cell response in trastuzumab plus chemotherapy treated patients, we profiled peripheral CD3+ T cells using 10x Genomics VDJ single-cell sequencing in paired samples from five patients with HER2+ breast cancer. Patients had stage IIA (n=2), stage IIIC (n=2) or stage IV (n=1) breast cancer and were treated with preoperative docetaxel, carboplatin, trastuzumab, pertuzumab (TCHP). Two patients had a pathological complete response (pCR), and three patients had partial clinical response with residual disease at surgery. Peripheral blood mononuclear cells (PMBCs) were collected at a C1D1 pre-treatment and day 1 of cycles 3, 4, or 5. Results: Eleven T cell subpopulations, including naïve and memory CD4+ and CD8+ T cells, activated CD4+ and CD8+ T effector cells, activated CD4+ T regulatory cells, were characterized in the five patients’ peripheral blood based on their transcriptional profiles. T cell subpopulation distribution and clonal expansion profiles were similar in pre- and post- treatment samples in all five donors. Large T cell clonal expansions were detected in the peripheral blood of the two patients who had a pCR, but were not detected in the three patients who had residual disease at surgery. The patients who had a pCR exhibited large expansions in activated CD8+ terminal effector memory/effector memory (TEM/EM) cells followed by expansions in activated CD4+ TEM/EM cells. A minor increasing trend in activated CD4+ Treg cells was observed across all patients upon treatment with TCHP. Conclusions: Single-cell sequencing enables high-resolution characterization of immune cell subsets and represents a promising approach to assess the immune response to trastuzumab and other cancer therapeutics. In this study, single-cell sequencing of peripheral CD3+ T cells identified clonal expansions in activated CD8+ and CD4+ T cells in HER2+ breast cancer patients who had a pCR with preoperative TCHP treatment. These data are consistent with the model that T cells play a key role in trastuzumab-mediated tumor control, and warrant further investigation in a larger sample population. Citation Format: John Vivian, Kimberly Walter, Elliott Drabek, Nicole Haaser, Maren K. Levin, Esther San Roman Rodriguez, Kendra Peck, Ngan Nguyen, Carl Millward, Jonathan Benjamin, William H. Robinson, Joyce A. O'Shaughnessy. Single-cell sequencing of the blood T cell repertoire before and after trastuzumab treatment in early stage HER2+ 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 P2-01-11.

Background LIV-1, a transmembrane protein and downstream target of STAT3, is highly expressed in breast cancer cells. It is associated with lymph node involvement and metastatic progression. SGN-LIV1A is an anti-LIV-1 antibody conjugated via a protease-cleavable linker to monomethyl auristatin E (MMAE). Upon binding to cell-surface LIV-1, SGN-LIV1A is internalized and releases MMAE, which disrupts microtubulin and induces apoptosis. Methods This ongoing, phase 1 study evaluates safety, tolerability, pharmacokinetics, and antitumor activity of SGN-LIV1A (q3wks IV) in women with LIV-1-positive, unresectable, locally advanced or metastatic breast cancer (LA/MBC) (NCT01969643). Patients (pts) with measurable disease and ≥2 prior cytotoxic regimens for LA/MBC are eligible. Pts with ≥ Grade 2 neuropathy are excluded. Response is assessed per RECIST v1.1; pts with stable disease (SD) or better can continue treatment until disease progression or intolerable toxicity. At completion of dose escalation in hormone receptor-positive/HER2-negative (HR+/HER2–) and triple-negative (TN) pts, expansion cohorts were opened to further evaluate safety and antitumor activity of monotherapy in TN pts. Tumor biopsies are evaluated for LIV-1 expression. Results To date, 69 pts (18 HR+/HER2–, 51 TN) have received a median of 3 cycles (range, 1–12) of SGN-LIV1A at doses of 0.5–2.8 mg/kg. Median age was 56 yrs. Pts had a median of 3 prior cytotoxic regimens for LA/MBC; 58 had visceral disease and 37 had bone metastases. No dose-limiting toxicities (DLTs) occurred in 19 DLT-evaluable pts; maximum tolerated dose was not exceeded at 2.8 mg/kg. Expansion cohorts of TN pts were opened at 2.0 and 2.5 mg/kg. Treatment-emergent adverse events (AEs) reported in ≥25% of pts were fatigue (59%), nausea (51%), peripheral neuropathy (44%), alopecia (36%), decreased appetite (33%), constipation (30%), abdominal pain, diarrhea, and neutropenia (25% each). Most AEs were Grade 1/2; AEs ≥ Grade 3 included neutropenia (25%) and anemia (15%). Febrile neutropenia occurred in 2 pts whose total dose exceeded 200 mg per cycle, including 1 treatment-related death due to sepsis. No other treatment-related deaths occurred on-study. Seven pts discontinued treatment due to AEs. In dose escalation, activity was observed in 17 efficacy evaluable (EE) HR+/HER2- pts, with a disease control rate (DCR= CR+PR+SD) of 59% (10 SD), including 1 pt with SD ≥24 wks. Among the 44 EE TN pts (dose escalation plus expansion cohorts), the objective response rate (ORR) was 32% (14 PR) with a confirmed PR rate of 21%, DCR was 64% (14 PR, 14 SD), and clinical benefit rate (CBR=CR+PR+SD ≥24 wks) was 36% (16 pts). For TN pts, median PFS was 11.3 wks (95% CI: 6.1, 17.1); 10 pts remain on treatment. Of 631 MBC tumor samples of all clinical subtypes evaluated for LIV-1, 91% were positive; 75% had moderate-to-high expression (H-score ≥100). Conclusions LIV-1 is expressed in almost all MBC tumors. SGN-LIV1A monotherapy was generally well tolerated and showed encouraging antitumor activity in heavily pretreated TN MBC, with a PR rate of 32%, confirmed PR rate of 21%, and CBR (≥24 wks) of 36%. Response duration data continue to evolve. Enrollment continues in the TN monotherapy expansion cohort. Citation Format: Modi S, Pusztai L, Forero A, Mita M, Miller KD, Weise A, Krop I, Burris III H, Kalinsky K, Tsai M, Liu MC, Hurvitz SA, Wilks S, Ademuyiwa F, Diab S, Han HS, Kato G, Nanda R, O'Shaughnessy J, Kostic A, Li M, Specht J. Phase 1 study of the antibody-drug conjugate SGN-LIV1A in patients with heavily pretreated triple-negative metastatic breast cancer [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr PD3-14.

Background: Metastatic TNBC has an aggressive course with limited therapy options and poor survival. Sacituzumab govitecan (IMMU-132) is a novel antibody drug conjugate consisting of SN-38, the active metabolite of the topoisomerase I inhibitor, irinotecan, conjugated to a humanized mAb targeting Trop-2, which is highly expressed in most epithelial cancers, including TNBC. We previously reported that patients (pts) with mTNBC treated with IMMU-132 after a median of 5 prior therapies from initial diagnosis achieved a 30% objective response rate (ORR), 8.9 mo median duration of response (DOR), and an acceptable safety profile with nausea, neutropenia, and diarrhea the most common toxicities (Bardia et al., JCO, 2017). IMMU-132 was awarded Breakthrough Designation by the FDA based on this data. Accordingly, we are enrolling additional patients with relapsed/refractory mTNBC with intention of seeking regulatory approval as a ≥3rd-line therapeutic option. Trial design: An international, open-label, Phase III study in pts with refractory/relapsed mTNBC after ≥2 prior chemotherapies for advanced disease or >1 therapy for pts who progress within 12 months of adjuvant therapy (NCT02574455). Pts are randomized 1:1 to receive either IMMU-132 (10 mg/kg IV, days 1 and 8 every 21 days) or TPC from one of 4 prespecified single-agent regimens (capecitabine, eribulin, vinorelbine or gemcitabine). Pts continue treatment until progression requiring discontinuation or unacceptable toxicity. The primary endpoint is progression-free survival (PFS) and additional endpoints include overall survival (OS), ORR, DOR, safety and quality of life. Independent, blinded reads of scans will be performed. Eligibility criteria: Adults >18 yrs old, with metastatic breast cancer, triple-negative by most recent biopsy, measurable disease by CT or MRI as per RECIST1.1, ECOG performance score 0 or 1, adequate safety laboratories. Refractory/relapsed after ≥2 prior standard chemotherapy regimens for advanced disease, or >1 therapy for pts who progress within 12 months of adjuvant therapy. Pts must have received taxane and be eligible by investigator to receive at least one of the TPC agents. Pts with treated, non-progressive brain metastases are eligible. Specific aims: To compare IMMU-132 to TPC as measured by PFS, OS, ORR, DOR,QOL, adverse events, safety laboratories, incidence of dose delays and reductions, and treatment discontinuations due to toxicity. Statistical methods: Assuming a median PFS of 3 mo. and OS of 10 mo. with TPC vs. 5 and 15 mo. with IMMU-132, respectively, a study size of 328 patients has >95% and >80% power to detect a statistically significant difference in PFS and OS, respectively, between the two treatment arms. Present accrual and target accrual: Trial enrollment will begin prior to SABCS 2017 with approximately 328 patients expected to be enrolled over 18 months at approximately 100 institutions in North America, Europe and potentially elsewhere. Contact: Immu132@Immunomedics.com Citation Format: Bardia A, Rugo HS, Horne H, Wegener WA, Goldenberg DM, O'Shaughnessy J. A phase III, randomized trial of sacituzumab govitecan (IMMU-132) vs treatment of physician choice (TPC) for metastatic triple-negative breast cancer (mTNBC) [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr OT2-07-05.

This abstract was withdrawn by the authors.

Background: The international, randomized, placebo-controlled phase III ExteNET trial showed that 1 year of neratinib after trastuzumab-based adjuvant therapy significantly improved 2-year invasive disease-free survival (iDFS) in early-stage HER2+ breast cancer (HR 0.67; 95% CI 0.50–0.91; p=0.009) [Chan et al. Lancet Oncol 2016]. The significant iDFS benefit with neratinib was maintained after a median of 5 years' follow-up (HR 0.73; 95% CI 0.57-0.92; p=0.008) [Martin et al. ESMO 2017]. We present exploratory analyses from the ExteNET trial examining the effects of the interval between completion of trastuzumab and randomization to commence neratinib on iDFS. Methods: Women with early-stage HER2+ breast cancer were randomly assigned to oral neratinib 240 mg/day or placebo for 1 year after standard primary therapy and trastuzumab-based adjuvant therapy. Under the original study protocol, (neo)adjuvant trastuzumab was to be completed ≤24 months before randomization; this was revised to ≤12 months before randomization after the NCCTG-N9831/NSABP B-31 4-year analysis showed that the risk of relapse is greatest during the first 12 months after completing trastuzumab. Disease recurrences were collected prospectively during 1 and 2 years post-randomization, and from medical records during 3–5 years post-randomization. Patients randomized ≤12 months after completion of adjuvant trastuzumab were further separated to look at those who initiated neratinib ≤6 months of completing adjuvant trastuzumab. Primary endpoint: iDFS. HR (95% CI) estimated using Cox proportional-hazards models. Data cut-off: March 1, 2017. Clinicaltrials.gov: NCT00878709. Results:The intention-to-treat population comprised 2840 patients (neratinib, n=1420; placebo, n=1420). Median time from last trastuzumab dose to randomization was 4.4 and 4.6 months in the neratinib and placebo groups, respectively. 81% of patients were randomized ≤12 months of completing trastuzumab. The effects of the interval between the last dose of trastuzumab and randomization/initiation of neratinib on iDFS after a median follow-up of 5.2 years are shown in the table. Estimated 5-year iDFS rate, % P-valueInterval from last dose of trastuzumab to randomizationnNeratinibPlaceboHR (95% CI)a(2-sided)≤6 months164190.085.40.62 (0.46–0.84)0.002≤12 monthsb229789.786.50.70 (0.54–0.90)0.006>12 monthsb54392.392.61.00 (0.51–1.94)0.992a. Neratinib vs placebo; b. Protocol-defined subgroups Conclusions: In ExteNET, patients who initiated neratinib within 12 months of completing trastuzumab-based adjuvant therapy appeared to derive greater benefit from treatment than those who started neratinib later. Further, exploratory analyses suggest that the magnitude of benefit with neratinib is greater if initiated sooner (i.e. within 6 months of completing trastuzumab). Given the benefits of neratinib overall in those initiating treatment ≤12 months from the end of adjuvant trastuzumab, extended adjuvant treatment with neratinib should be initiated early following completion of trastuzumab. Citation Format: Ejlertsen B, Chan A, Gnant M, von Minckwitz G, Delaloge S, Buyse M, O'Shaughnessy J, Mansi J, Moy B, Iwata H, Wong A, Ye Y, Means-Powell J, Hui R, Ruiz-Borrego M, Ruiz Simon A, Shen Z-Z, Holmes FA, Lesniewski-Kmak K, Martin M. Timing of initiation of neratinib after completion of trastuzumab-based adjuvant therapy in early-stage HER2+ breast cancer: Exploratory analyses from the phase III ExteNET trial [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P1-13-05.

Background: mTNBC has an aggressive course with limited therapeutic options. Sacituzumab govitecan (IMMU-132) is a novel antibody drug conjugate consisting of SN-38, the active metabolite of the topoisomerase I inhibitor, irinotecan, conjugated to a humanized mAb targeting Trop-2, which is highly expressed in most epithelial cancers, including TNBC. A phase I/II basket trial (NCT01631552) was conducted in patients (pts) with multiple, advanced epithelial cancers. We previously reported preliminary results in mTNBC (N=69; objective response rate [ORR] = 30%, Bardia et al., JCO 2017;35:2141-2148). In 2016, sacituzumab govitecan was granted Breakthrough Designation based on this encouraging data, and we resumed enrollment in a more defined patient population (≥3rd-line setting in mTNBC). Methods: Pts received sacituzumab govitecan on days 1 & 8 of a 21-day cycle until progression or unacceptable toxicity. Eligibility included > 2 prior lines of therapy for metastatic disease, measurable disease by CT or MRI and prior taxane. Efficacy was assessed locally by RECIST 1.1 and confirmed by independent centralized blinded review. ORR, DOR, progression-free survival (PFS) and overall survival (OS) were determined. Adverse events (CTCAE v4.0), immunogenicity, and Trop-2 expression in archived tumor samples, when available, were evaluated. Results: 110 mTNBC pts (109 female, 1 male; median age 55 yrs, range 31-81), including 53 from the previously reported cohort of 69 pts who had received ≥2 prior regimens for metastatic disease, were accrued between 7/2013 and 2/2017. As of data cutoff on 6/30/2017, 71 are deceased, 23 in long-term follow-up, and 16 still on treatment. All pts were treated at the 10 mg/kg IMMU-132 dose level, receiving 14.5 median doses (range 1-88). Treatment was well tolerated, with no treatment-related deaths, 2 treatment discontinuations for toxicity, and no anti-drug antibodies detected. Grade ≥ 3 toxicity (≥10%) included neutropenia, 39%; leukopenia, 14%; anemia, 10%; the incidence of febrile neutropenia was low (7%). By local radiologist assessment, the ORR is 34% (37/110), including 3 CRs and 34 PRs, the clinical benefit rate (CBR: CR+PR+SD>6 mo.) is 46%, the KM median DOR and PFS are 7.6 mo. (95% CI: 4.8 to 11.3) and 5.5 mo. (95% CI: 4.8 to 6.6), respectively, including 10% (11 pts) with long-term PFS (12 to 30+ mo.), and the KM median OS is 12.7 mo. (95% CI: 10.8 to 13.6). Results of the independent central blinded review along with sensitivity analyses of prior treatment regimens, including checkpoint inhibitor use, and exploratory biomarker analysis of Trop-2 expression will be presented at the meeting. Conclusions: Sacituzumab govitecan demonstrated significant clinical activity as a single agent in the ≥3rd-line setting for patients with relapsed/refractory mTNBC. Given the high unmet medical need, data from this trial is being submitted for consideration of accelerated approval, and a global confirmatory randomized Phase III trial (NCT02574455) is underway. Additional studies including rational combinations are currently being evaluated for mTNBC and other breast cancer subsets. Citation Format: Bardia A, Vahdat LT, Diamond J, Kalinsky K, O'Shaughnessy J, Moroose RL, Isakoff SJ, Tolaney SM, Santin AD, Abramson V, Shah NC, Govindan SV, Maliakal P, Sharkey RM, Wegener WA, Goldenberg DM, Mayer IA. Sacituzumab govitecan (IMMU-132), an anti-Trop-2-SN-38 antibody-drug conjugate, as ≥3rd-line therapeutic option for patients with relapsed/refractory metastatic triple-negative breast cancer (mTNBC): efficacy results [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr GS1-07.