Abstract PD3-02: Incidence of late relapse in HER2-positive (HER2+) breast cancer patients receiving adjuvant trastuzumab: Combined analysis of NCCTG (Alliance) N9831 and NSABP (NRG) B31

Background: Recent trials showed potential benefit of extended adjuvant endocrine therapy and relatively high risk of relapse after 5 years (yr) in hormone receptor-positive (HR+) HER2- breast cancer. While risk of late relapse in HR+ HER2- is fairly well defined, the risk of late relapse in HER2+ remains largely unknown. Method: 4547 HER2+ patients treated with adjuvant chemotherapy alone or combined with trastuzumab (TH) were included (3132 from North Central Cancer Treatment Group [NCCTG, now Alliance] N9831; 1415 from National Surgical Adjuvant Breast and Bowel Project [NSABP, now NRG] B-31). Intrinsic subtypes were assessed by Prosigna test. Kaplan-Meier method and Cox proportional hazards model were used for analysis. Results: Median follow-up was 10.4 yr in N9831 and 7.0 yr in NSABP-B31. 54.5% of pts had HR+ disease. Pts were classified as HER2 enriched (77.4%), Luminal B (10.1%), Luminal A (7.7%), and Basal (4.8%). In multivariate Cox regression analysis in both treatment groups, HR+ was significantly associated with improved recurrence-free survival (RFS) during the first 5 yr (HR 0.65, 95% CI 0.56-0.77, p Support: U10CA180821, U10CA18082, U24CA196171; U10CA180868, UG1CA189867, U10CA180822, U24CA196067; ClinicalTrials.gov Id:NCT00005970, NCT00004067 Citation Format: Chumsri S, Li Z, Serie DJ, Mashadi-Hossein A, Colon-Otero G, Song N, Pogue-Geile K, Gavin P, Paik S, Moreno-Aspitia A, Perez EA, Thompson EA. Incidence of late relapse in HER2-positive (HER2+) breast cancer patients receiving adjuvant trastuzumab: Combined analysis of NCCTG (Alliance) N9831 and NSABP (NRG) B31 [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 PD3-02.