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 < 25 (NCT01272037). Methods: Eligibility criteria included women > 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 < 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<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 < 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) < 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.