Perez, Edith A.

Abstract Background Anthracycline use in metastatic breast cancer (MBC) is hindered by cumulative exposure limits and risk of cardiotoxicity. Pixantrone, a novel aza-anthracenedione with structural similarities to mitoxantrone and anthracyclines, is theorized to exhibit less cardiotoxicity, mainly due to lack of iron binding. We conducted a randomized phase II study to evaluate the efficacy and safety of 2 dosing schedules of pixantrone in patients with refractory HER2-negative MBC. Methods Intravenous pixantrone was administered at 180 mg/m2 every 3 weeks (group A) versus 85 mg/m2 on days 1, 8, and 15 of a 28-day cycle (group B). Primary endpoint was objective response rate (ORR) and secondary endpoints included progression-free survival (PFS), median 6-month PFS, overall survival (OS), safety, quality of life, and serial assessment of circulating tumor cells. A 20% ORR was targeted as sufficient for further testing of pixantrone in this patient population. Results Forty-five patients were evaluable, with 2 confirmed partial responses in group A and 1 in group B. The trial was terminated due to insufficient activity. Overall median PFS and OS were 2.8 (95% confidence interval [CI]: 2.0-4.1) and 16.8 (95% CI: 8.9-21.6) months, respectively. Notable overall grade 3-4 adverse events were the following: neutrophil count decrease (62%), fatigue (16%), and decrease in ejection fraction (EF) (4%). Conclusion Pixantrone has insufficient activity in the second- and third-line MBC setting. It appears, however, to have limited cardiotoxicity. (ClinicalTrials.gov ID: NCT01086605).

Abstract Background: A previous neoadjuvant study in patients with triple negative breast cancer (TNBC) demonstrated that low tumor infiltrating lymphocytes (TILs) after neoadjuvant chemotherapy is associated with a poor outcome. Activation of RAS/MAPK pathway has been associated with reduced TILs. Preclinical studies showed that MEK inhibitor enhances immune responses and is synergistic with anti PD-1/PD-L1 therapy in TNBC. Methods: The standard Phase I 3+3 study design was used. Patients with unresectable locally advanced or metastatic TNBC with ≤ 3 prior lines of therapy were enrolled. Patients received single agent binimetinib for 2 weeks prior to an addition of pembrolizumab. Dose level 0 was binimetinib at 45 mg oral twice daily continuously and dose level -1 was 30 mg twice daily. Pembrolizumab was given at a fixed dose of 200 mg every 3 weeks in both dose levels. The maximum tolerated dose (MTD) was defined as the dose level below the lowest dose that induces dose-limiting toxicity (DLT) during the first 2 cycles in at least one-third of patients. Results: A total of 12 evaluable patients were enrolled in the phase I, 4 patients in dose level 0 and 8 patients in dose level -1. In dose level 0, among 3 out of 4 patients who were evaluable for DLT, 2 patients experienced DLTs, including grade (G) 3 nausea, vomiting, abdominal pain and G3 ALT elevation. Thus, the stopping rule was met and the dose level was adjusted to dose level -1. None of the first 3 patients in dose level -1 experienced a DLT. All three experienced other ≥ G3 AEs, including 1 G3 cardiac troponin T increased and 2 with G3 hypertension. 5 additional patients were accrued to dose level -1 and were evaluable for AEs. Three of these were evaluable for DLTs. One patient had G3 ALT/AST increase, deemed a DLT. However, this patient had liver metastasis and had G1 ALT/AST elevation at baseline. Her ALT/AST normalized in 3 weeks after treatment discontinuation and oral prednisone. Other ≥ G3 toxicities in the second group of 5 patients in dose level -1 include G3 hypertension (12.5%), nausea (12.5%), hypokalemia (12.5%), neutrophil count decrease (12.5%) dyspnea (12.5%), peripheral neuropathy (12.5%), and retinal detachment (12.5%). Since less than 1/3 of patients experienced DLT and there was no ≥ G4 AE at least possibly related to treatment over all cycles at any given dose level, the MTD was determined as dose level -1. Five patients are currently enrolled in the phase II section, and 10 more patients are needed. Objective response rate analysis will be performed once study enrollment is completed. Conclusions: The recommended phase II doses for pembrolizumab in combination with binimetinib are 200 mg every 3 weeks and 30 mg twice daily, respectively. The combination appears to be safe with manageable toxicities. Long term durable response has been observed. The phase 2 portion of this trial is currently on going. Citation Format: Saranya Chumsri, Jun He, David Hillman, Morgan Weidner, Morgan Weidner, Dana Haley, Aline Reis, Kathleen Tenner, Pooja Advani, Kostandinos Sideras, Alvaro Moreno-Aspitia, Edith Perez, Keith Knutson. Results of phase I study of pembrolizumab in combination with binimetinib in patients with unresectable locally advanced or metastatic triple negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr CT133.

2549 Background: BDC-1001 is a novel ISAC consisting of an investigational trastuzumab biosimilar chemically conjugated to a TLR 7/8 agonist with a non-cleavable linker. BDC-1001 was designed to activate the innate immune system, eliciting antibody-mediated effector functions (eg, antibody-dependent cellular phagocytosis) and a durable adaptive immune response. In preclinical tumor models resistant to anti-HER2 treatments, BDC-1001 demonstrated potent and durable immune-mediated antitumor efficacy. Methods: A 4-part, phase 1/2 dose-escalation/expansion study was initiated to evaluate BDC-1001 ± PD1 inhibitor pembrolizumab in pts with HER2-expressing solid tumors who had progressive disease on standard of care (NCT04278144). Preliminary results of the monotherapy dose escalation (Part 1) are reported. Pts with advanced metastatic HER2-expressing (IHC2/3+) or amplified solid tumors received BDC-1001 IV q3w in a 3+3 design w/ 12 pts/cohort backfill allowed. Primary objectives were to evaluate safety, tolerability, dose-limiting toxicities (DLTs) and determine a phase 2 dose; secondary objectives were to assess pharmacokinetics (PK), pharmacodynamics and preliminary anti-tumor activity. Results: As of Jan 29, 2021, 20 pts w/ a median age of 65 (46-85) have enrolled in 4 dose levels (0.15mg/kg to 5 mg/kg). Cancer types include breast, biliary, cervical, colorectal (CRC), lung, gastroesophageal, salivary, urinary tract and endometrial. Pts had received a median of 4 (1-7) prior therapies; 65% received >1 prior anti-HER2 therapy. All pts completed the 21-day DLT period; no DLTs or drug-related serious adverse events (AEs) have been observed. AEs deemed related to BDC-1001 have been mild to moderate including infusion-related reactions. The MTD has not been reached (treatment duration 5-17+wk); enrollment is ongoing. PK evaluations showed Cmax levels consistent with predicted modeling based on non-human primates (NHP). One pt with microsatellite stable (MSS) HER2+ CRC with lung metastases had a confirmed partial response after 4 cycles and remains on study; 2 additional pts with metastatic MSS HER2+ CRC had stable disease (SD) and a pt with heavily pretreated MSS endometrial cancer with lung metastases had confirmed SD and remains on treatment 17+ wk; 3 of these pts had received 2 prior anti-HER2 therapies. Conclusions: In this first-in-human study, BDC-1001 appears to be well-tolerated up to the dose tested to date (5 mg/kg), with Cmax levels achieved as predicted by NHP modeling. Evidence of clinical activity have been observed, including in pts previously treated with anti-HER2 therapy. Dose escalation is ongoing and will be followed by combination dosing with CPI and the phase 2 component in selected tumors. Clinical trial information: NCT04278144.

535 Background: Invasive lobular carcinoma (ILC) is a rarer form of breast cancer, accounting for 10% of the disease cases. HER2 overexpression in ILC is infrequent and limited data exist regarding clinical characteristics and outcome of HER2-positive (HER2+) ILC patients (pts) treated with adjuvant trastuzumab. Methods: Patient characteristics were compared between ILC and invasive ductal carcinoma (IDC) using Wilcoxon rank sum test for continuous variables and Chi-square test for categorical variables. Kaplan-Meier (KM) method was used to estimate the freedom from mortality and recurrence. Cox regression model was used to evaluate the association between ILC and outcomes adjusted for other characteristics. NanoString technology was used to quantify mRNA to develop immune-related gene signatures. Results: From a total of 3,304 pts, 122 (3.7%) pts had ILC. Pts with ILC were significantly older (median age 54 vs. 49 years), had larger tumors, lower grade, more ER and PR positive tumors, and more lymph node involvement (25.4% had N3 disease compared to 12.7% in IDC). Overall, with KM analysis, pts with ILC had significantly worse overall survival (OS, p = 0.005) and recurrence-free survival (RFS, p = 0.046) compared to IDC. The 15-year freedom from recurrence was merely 57.67% in ILC compared to 72.68% in IDC. A significant number of hormone receptor-positive (HR+) ILC pts developed late recurrence with cumulative event rates increasing from 23% at 5 years to 42% at 15 years. Nevertheless, in multivariate Cox regression analysis adjusting for other clinical characteristics, including age, tumor size, grade, ER/PR, and lymph node status, lobular histology was not significantly associated with worse outcome for OS (HR = 1.19, 95%CI 0.67-2.1, p = 0.55) and RFS (HR = 1.5, 95%CI 0.9-2.5, p = 0.12), as compared with IDC. However, ILC pts appeared to have similar degree of benefit from trastuzumab, with RFS HR = 0.58 compared to HR = 0.67 in the entire population. For immune landscape, there was no significant difference in gene signatures related to CD45, CD8, B cells, or cytotoxic cells. However, ILC had more enrichment in mast cell gene signature and fewer macrophage, NK CD56dim, and regulatory T cell signatures compared to IDC (p < 0.05). Conclusions: HER2+ ILC has distinct clinical characteristics and immune landscape compared to IDC. ILC pts appeared to have worse outcome compared to IDC likely because ILC pts often presented with more locally advanced disease. However, similar benefit of trastuzumab was observed in ILC pts. Due to high risk of late relapse in HR+ HER2+ ILC, extended adjuvant endocrine therapy should be considered in this group of high-risk pts. Clinical trial information: NCT00005970.

Background: The management of patients with triple-negative breast cancer (TNBC) is challenging with several controversies and unmet needs. During the 12th Breast-Gynaecological & Immuno-oncology International Cancer Conference (BGICC) Egypt, 2020, a panel of 35 breast cancer experts from 13 countries voted on consensus guidelines for the clinical management of TNBC. The consensus was subsequently updated based on the most recent data evolved lately. Methods: A consensus conference approach adapted from the American Society of Clinical Oncology (ASCO) was utilized. The panellists voted anonymously on each question, and a consensus was achieved when ≥75% of voters selected an answer. The final consensus was later circulated to the panellists for critical revision of important intellectual content. Results and conclusion: These recommendations represent the available clinical evidence and expert opinion when evidence is scarce. The percentage of the consensus votes, levels of evidence and grades of recommendation are presented for each statement. The consensus covered all the aspects of TNBC management starting from defining TNBC to the management of metastatic disease and highlighted the rapidly evolving landscape in this field. Consensus was reached in 70% of the statements (35/50). In addition, areas of warranted research were identified to guide future prospective clinical trials.

Abstract Background: Overall, patients with cancer experience a greater risk of adverse outcomes following SARS-CoV-2 infection; however, little is known for those with BC. Methods: CCC19 (NCT04354701) is an international cohort study aimed at investigating the impact of COVID-19 in patients with a history of or active cancer using de-identified data on patient demographics, cancer history, clinical course and outcomes of COVID-19. The current analysis includes patients from U.S. and Canada with invasive BC and laboratory-confirmed SARS-CoV-2 entered between March 17, 2020 and July 2, 2020. Co-primary outcomes were hospitalization during COVID-19 illness and 30-day all-cause mortality. Frequencies for categorical variables and medians (range) for continuous variables were estimated. Final presentation will include bivariable and multivariable Cox proportional hazards regression analysis to identify risk factors (including BC subtypes and therapies, for which data collection is ongoing) associated with 30-day all-cause mortality and severe COVID-19 illness (composite of any hospitalization requiring supplemental oxygen, admission to an intensive care unit [ICU], use of mechanical ventilation, or death). Results: During the study period, a total of 2683 patients with cancer and COVID-19 were accrued in the CCC19 registry including 529 (20%) with invasive BC. Among patients with BC, 352 (67%) were 60 years or older; 518 (98%) were women; 275 (52%) non-Hispanic White, 116 (22%) non-Hispanic Black, 70 (13%) Hispanic, 56 (11%) in other categorizations; 178 (34%) had a smoking history; 75 (14%) ECOG performance status ≥2; 191 (36%) with &gt;2 active comorbidities; 64 (12%) with AJCC stage IV disease at BC diagnosis; and 267 (50%) were on anti-cancer treatment including systemic therapy, radiation, or surgery within 3 months of COVID-19 diagnosis. At least 323 (61%) patients with BC had 30-day follow-up after COVID-19 diagnosis, and 35 (7%) had 90-day follow-up. COVID-19 illness at initial diagnosis required outpatient care in 288 (54%), inpatient care in 193 (36%), and ICU care in 40 (8%). Overall, 247 (47%) were hospitalized and 30-day all-cause mortality was 9%. 30-day all-cause mortality rates by receipt of major BC treatment modalities (within past 3 months) were: 10% for those on cytotoxic systemic therapy vs 5% and 12% for noncytotoxic systemic therapy and local therapy, respectively. The table shows hospitalization and mortality outcomes by major demographic and BC treatment strata. The final presentation will incorporate the latest patient accrual and evaluate independent clinical risk factors associated with serious COVID-19 outcomes in patients with BC. Conclusions: This represents the largest study to date of COVID-19 outcomes in patients with invasive BC. Nearly half of the patients with BC required hospitalization during their COVID-19 disease course and we observed a 9% 30-day all-cause mortality. Submitted on behalf of the COVID-19 and Cancer Consortium (ccc19us.org) Table 1. COVID-19 related hospitalization and 30-day all-cause mortality for all patients with invasive BCNAny Hospitalization30-day all-cause MortalityN% [95% CI]N% [95% CI]Total population52924747 [42-51]499 [7-12]Age&lt;601774425 [19-32]21 [0-4]60-691155144 [35-54]87 [3-13]70-791206655 [46-64]1714 [8-22]80+1178674 [65-81]2219 [12-27]ECOG PS0-132212238 [33-43]165 [3-8]2+756181 [71-89]1621 [13-32]Active Comorbidities0741014 [7-23]00 [0-5]1-22239442 [36-49]178 [5-12]&gt;219112968 [60-74]2915 [10-21]Treatment IntentCurative1866434 [28-42]95 [2-9]Palliative743953 [41-64]1216 [9-27]Cancer StatusRemission/NED33115447 [41-52]247 [5-11]Active disease, stable or responding to treatment1194840 [31-50]76 [2-12]Active disease, progressing372773 [56-86]1130 [16-47]Treatment Modality (within 3 months)Cytotoxic chemotherapy833542 [31-54]810 [4-18]Noncytotoxic therapy1856435 [28-42]105 [3-10]Local therapy (surgery or radiation)341750 [32-68]412 [3-27] Citation Format: Ali Raza Khaki, Dimpy P Shah, Maryam B Lustberg, Melissa K Accordino, Daniel G Stover, Gayathri Nagaraj, Donna R Rivera, Edith A Perez, Sara M Tolaney, Jeffrey Peppercorn, Petros Grivas, Jeremy L Warner, Corrie A Painter, Gilberto de Lima Lopes, Jr, Solange Peters, Michael A Thompson, Toni K Choueiri, Brian I Rini, Gary H Lyman, Nicole M Kuderer, Shaveta Vinayak. Characteristics and outcomes of SARS-CoV-2 infection in patients with invasive breast cancer (BC) from the COVID-19 and cancer consortium (CCC19) cohort study [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 PS7-01.

Abstract Background: Growing data established the pivotal role of preexisting immune response in triple negative breast cancer (TNBC). Conventionally, preexisting immune response can be evaluated by quantifying tumor infiltrating lymphocytes mainly in the stroma or gene expression analysis from the whole tumor section. Due to technical challenges with these conventional methods, limited data regarding specific subtypes and spatial distribution of these immune infiltrates are currently available. Methods: NanoString IO360 gene expression analysis and Digital Spatial Profiling (DSP) were used. DSP was used to quantify 29 immune-related proteins in stromal and tumor-enriched segments from 44 TNBC samples from the FinXX trial (NCT00114816) and 335 samples from the Mayo Clinic (MC) cohort of centrally reviewed TNBC (Leon-Ferre BCRT 2018). In FinXX trial, 22 patients with recurrence and 22 patients without recurrence were included. In MC cohort, 217/335 patients received adjuvant chemotherapy while 118 patients had surgery only without adjuvant chemotherapy. Regions were segmented based on pancytokeratin staining. The general linear model was used for statistical analysis of differential expression with recurrence free survival (RFS) as a categorical variable (recur yes or no). Kaplan-Meier (KM) estimates and Cox regression models were also used for analysis. Results: In the FinXX trial, there were 12 out of 29 proteins in tumor epithelial segments (intraepithelial) which were significantly expressed at higher levels among patients who were free of recurrence. These proteins include Beta-2 microglobulin, CD11c, CD20, CD40, CD56, CD8, Granzyme B, HLA-DR, ICOS, PD-L1, PD-L2, and TGFB1. In contrast, merely 5 out of 29 proteins in stromal segments were significantly differentially expressed in these 2 groups of patients. Granzyme B, IDO1, PD-L1, and PD-L2 in stroma were significantly higher and SMA was significantly lower in patients without recurrence. Using Cox regression models, intraepithelial CD56, CD40, and HLA-DR were significantly associated with outcome. When comparing between highest and lowest intraepithelial protein expression by tertile, intraepithelial CD56 (HR 0.12, 95%CI 0.03-0.39, p &lt; 0.001), CD40 (HR 0.13, 95%CI 0.04-0.46, p = 0.002), and HLA-DR (HR 0.24, 95%CI 0.06-0.89, p = 0.032) were significantly associated with improved outcome. However, expression of these same proteins in stroma was not associated with outcome. Using KM estimates, intraepithelial CD56 (p &lt; 0.0001), CD40 (p = 0.0006), and HLA-DR (p = 0.013) were also significantly associated with improved outcome. Nonetheless, RNA expression of these proteins by IO360 from whole tumor sections were not significantly associated with outcome (CD56 p = 0.27, CD40 p = 0.21, HLA-DR p = 0.48). Similar findings with DSP were observed in MC TNBC cohort. Comparing between the highest and lowest quartiles, there were significantly fewer patients who developed recurrence with high protein expression of intraepithelial CD56 (p &lt; 0.001), CD40 (p = 0.002), and HLA-DR (p = 0.006). Conclusions: Using an in-depth analysis with spatially defined context, we identify that there were numerically more intraepithelial immune-related proteins associated with outcome compared to proteins in stroma. Specifically, intraepithelial CD56, CD40, and HLA-DR were significantly associated with improved outcome in both FinXX and MC TNBC cohorts. However, neither expression of these proteins in stroma nor RNA expression from whole tumor were associated with outcome. Our study highlights the impact of spatial biology and the importance of evaluating each potential biomarker in a spatially defined manner. Support: W81XWH-15-1-0292, BCRF 19-161, P50CA116201-9, P50CA015083 Citation Format: Saranya Chumsri, Jodi M. Carter, Yaohua Ma, Douglas Hinerfeld, Heather Ann Brauer, Sarah Warren, Torsten O. Nielsen, Karama Asleh, Heikki Joensuu, Edith A. Perez, Roberto A. Leon-Ferre, David W. Hillman, Judy C. Boughey, Minetta C. Liu, James N. Ingle, Krishna R. Kalari, Fergus J. Couch, Keith L. Knutson, Matthew P. Goetz, E. A. Thompson. Spatially defined immune-related proteins and outcome in triple negative breast cancer in the FinXX trial and Mayo Clinic cohort [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 PS6-02.

Abstract Background: Although risk of late relapse in hormone receptor-positive (HR+) breast cancer is well established, most existing data pertain to the HR+ HER2-negative (HER2-) subgroup. CTS5 is one of the models for predicting risk of late relapse in HR+ HER2- breast cancer. However, the value of this model in HR+ HER2+ disease is less known, particularly in the context of adjuvant trastuzumab. Here, we evaluated CTS5 in patients with early stage HR+ HER2+ breast cancer treated in the NCCTG N9831 (Alliance for Clinical Trials in Oncology) and NSABP B-31 (NRG) trials. Methods: Stage I-III HR+ (ER+ and/or PR+) HER2+ breast cancer patients who were free of recurrence after 5 years in N9831 and B-31 trials were included. The online CTS5 calculator was used to determine CTS5 score and risk group (low, intermediate, and high) based on age, tumor size, grade, and number of involved nodes. Kaplan-Meier (KM) estimates, Cox regression models, and C index were used for analysis. N9831 and B-31 trials were analyzed separately. Results: 1,204 patients in N9831 and 658 patients in B-31 met the entry criteria. Baseline characteristics were similar between both trials, including median age, tumor size, and follow up. Similar distribution within CTS5 risk group was observed in both trials; 68.2% and 70.1% patients were high risk, 24% and 21.9% as intermediate risk, as well as 7.8% and 8.1% as low risk classified in N9831 and B-31, respectively. Using univariate Cox regression analysis, CTS5 score as a continuous variable was associated with recurrence-free survival (RFS) in the entire study cohort, including patients who received chemotherapy alone or in combination with trastuzumab, (HR 1.37, 95%CI 1.03-1.81, p=0.03, C index 0.57 in N9831 and HR 1.36, 95%CI 1.06-1.76, p=0.02, C index 0.54 in B-31), but not in patients who received concurrent trastuzumab (HR 1.19, 95%CI 0.73-1.2, p=0.49, C index 0.54 in N9831 and HR 1.35, 95%CI 0.96-1.9, p=0.08, C index 0.54 in B-31). As categorical variable in the entire study cohort, CTS5 risk group was not significantly associated with RFS among patients with intermediate vs. low (HR 0.47, 95%CI 0.18-1.22, p=0.12 and HR 1.61, 95%CI 0.66-3.92, p=0.29) and high vs. low (HR 1.23, 95%CI 0.57-2.67, p=0.6 and HR 1.93, 95%CI 0.85-4.41, p=0.12) with the C index of 0.58 and 0.53 in N9831 and B-31 respectively. There was also no significant difference in RFS among 3 CTS5 risk groups with Kaplan-Meier estimates. Among patients who received concurrent trastuzumab, similar trends were observed with no statistical difference in RFS between high vs. low (HR 0.68, 95%CI 0.24-1.97, p=0.48 and HR 1.44, 95%CI 0.52-3.96, 0.49) with the C index of 0.55 and 0.51 in N9831 and B-31, respectively. Paradoxically, patients with intermediate risk had better RFS than low risk (HR 0.18, 95%CI 0.03-0.97, p=0.05) in N9831 but no significant difference in B-31 (HR 1.31, 95%CI 0.44-3.95, p=0.63). Conclusions: While CTS5 score as a continuous variable was associated with outcome in overall HR+ HER2+ population, this model was not prognostic in patients receiving adjuvant trastuzumab in both N9831 and B-31 trials. Furthermore, the correlation (C index) was modest and CTS5 risk group as a categorical variable could not stratify outcome in this group of patients. This study underlines the need to develop a new prognostic model to better delineate the risk of late relapse in HR+ HER2+ breast cancer patients receiving trastuzumab as this model can facilitate clinical decision for extended adjuvant endocrine therapy. Support: BCRF-19-161, U10CA180821, U10CA180868 and U10CA180822 (NRG), Genentech. https://acknowledgments.alliancefound.org Citation Format: Tanyami Pai, Angelica Gil, Yaohua Ma, Zhuo Li, Pooja Advani, Moreno Moreno-Aspitia, Gerardo Colon-Otero, Edith A. Perez, Yan Asmann, Katherine Pogue-Geile, E. A. Thompson, Saranya Chumsri. Prognostic value of clinical treatment score post-5 years (CTS5) and late relapse risk in hormone receptor-positive HER2-positive breast cancer in the North Central Cancer Treatment Group (NCCTG) N9831 (Alliance) and NSABP B-31 (NRG) trials [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 PS6-03.

Abstract Funding: Supported by National Cancer Institute grants U10CA180888, U10CA180819, U10CA180820, U10CA180821, U10CA180868, U10CA180863; and in part by Susan G. Komen for the Cure® Research Program, The Hope Foundation for Cancer Research, Breast Cancer Research Foundation, and Genomic Health, Inc. Acknowledgement: The authors wish to thank Dr. Ana M. Gonzalez-Angulo, MD, for her invaluable contributions to the design and implementation of this study. Background: The clinical utility of the RS to determine CT benefit is well established in pts with HR+, HER2-, axillary lymph node (LN)-negative BC. Retrospective analyses from SWOG S8814 support the potential prognostic and predictive role of RS for CT benefit in postmenopausal pts with LN+ BC. SWOG S1007 is a prospective, randomized trial of endocrine therapy (ET) vs. chemoendocrine therapy (CET) in women with 1-3 +LN and a RS &lt; 25 (NCT01272037). Methods: Eligibility criteria included women &gt; 18 years of age with HR+, HER2- BC and 1-3 +LN and no contraindications to taxane and/or anthracycline based CT. Women with a RS &lt; 25 were randomized to receive ET or CET in 1:1 randomization using 3 stratification factors: (1) RS (0-13 vs.14-25); (2) menopausal status; and (3) axillary nodal dissection vs. sentinel node biopsy. The primary objective was to determine the effect of CT on invasive disease-free survival (IDFS) and whether the effect depended on the RS. The primary analysis was to test for a significant interaction of the treatment arm and continuous RS using a Cox regression model for IDFS, adjusting for treatment, RS, and menopausal status. A total of 832 IDFS events were expected for the final analysis. Secondary objectives included overall survival (OS). The protocol specified that interaction between treatment and the stratification variables was to be tested and, if significant, separate analyses performed by stratum. Annual interim analyses were planned starting at 24% of events. At the third interim analysis with 410 IDFS events, the Data and Safety Monitoring Committee recommended reporting results, with a decision by the NCI’s Cancer Therapy Evaluation Program, the study sponsor. Results: Of the 9,383 women screened from 2/28/11-9/29/17, 5,083 pts (54.2%) were randomized. With a median follow-up of 5.1 years, 447 IDFS events have been observed. For the primary analysis, the interaction test for CT benefit and continuous RS was not statistically significant, p=0.30. In a model with CT, RS, and menopausal status (no interaction term), higher continuous RS was associated with worse IDFS [HR 1.06, 2-sided p&lt;0.001, 95% Confidence Interval (CI) 1.04-1.07], and CT was associated with an improvement in IDFS (HR 0.81, p=0.026, 95% CI 0.67-0.98). In a pre-specified analysis, a significant interaction was identified between CT and menopausal status (p=0.004), necessitating separate analyses by menopausal status. In postmenopausal pts (N=3350, 67%), adjusting for continuous RS, the HR for CET vs. ET was not significant (HR=0.97, p=0.82, 95% CI 0.78-1.22; 5-year IDFS 91.6% vs. 91.9%) indicating no benefit from CT. In premenopausal pts (N=1665, 33%), the HR (0.54) was statistically significant (p=0.0004, 95% CI 0.38-0.76; 5-year IDFS 94.2% vs. 89.0%), indicating CT benefit. In premenopausal pts, ovarian suppression was performed in 15.9% vs. 3.7% (ET vs. CET), and 47.9% vs. 26.4% reported menstruation after 6 months of treatment. Although the number of events is limited, the HR for treatment adjusted by RS for OS in premenopausal pts was 0.47 (p=0.032, 95% CI 0.24-0.94). At this time, there is no differential effect with CT in regard to other stratification factors. Conclusions: There is a significant differential treatment effect of CT benefit based on RS for premenopausal vs. postmenopausal women requiring separate analyses. While only 54% of the protocol specified events are recorded and pts will be followed for 15 years, the current data show that adjuvant therapy can be de-escalated to ET alone in postmenopausal pts with a RS &lt; 25 and 1-3 +LN. However, there is a strong IDFS benefit for CET in premenopausal pts, with an early indication of an OS improvement. Citation Format: Kevin Kalinsky, William E Barlow, Funda Meric-Bernstam, Julie R Gralow, Kathy S Albain, Daniel Hayes, Nancy Lin, Edith A Perez, Lori J Goldstein, Stephen Chia, Subkhbinder Dhesy-Thind, Priya Rastogi, Emilio Alba, Suzette Delaloge, Miguel Martín, Miguel Gil Gil, Claudia Arce-Salinas, Etienne Brain, In Hae Park, Jean-Yves Pierga, Ana Hernandez Lluch, Manuel Ramos Vasquez, Manuel Ruiz Borrego, Kyung Hae Jung, Jean-Marc Ferrero, Anne Schott, Steve Shak, Priyanka Sharma, Danika L Lew, Jieling Miao, Debu Tripathy, Gabriel Hortobagyi, Lajos Pusztai. First results from a phase III randomized clinical trial of standard adjuvant endocrine therapy (ET) +/- chemotherapy (CT) in patients (pts) with 1-3 positive nodes, hormone receptor-positive (HR+) and HER2-negative (HER2-) breast cancer (BC) with recurrence score (RS) &lt; 25: SWOG S1007 (RxPonder) [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr GS3-00.