Incidence of Late Relapses in Patients With HER2-Positive Breast Cancer Receiving Adjuvant Trastuzumab: Combined Analysis of NCCTG N9831 (Alliance) and NRG Oncology/NSABP B-31

Recent trials have shown potential benefit of extended adjuvant endocrine therapy and relatively high risk of recurrence (RoR) after 5 years in hormone receptor-positive (HR+) human epidermal growth factor receptor 2-negative (HER2-) breast cancer. Although risk of late relapse in HR+ HER2- breast cancer is fairly well defined, the risk in HER2-positive (HER2+) breast cancer treated with adjuvant trastuzumab-based chemotherapy remains largely unknown. We included 3,177 patients with HER2+ breast cancer treated with adjuvant chemotherapy alone or with trastuzumab from the North Central Cancer Treatment Group N9831 (ClinicalTrials.gov identifier: NCT00005970) and National Surgical Adjuvant Breast and Bowel Project B-31 (ClinicalTrials.gov identifier: NCT00004067) trials. Overall, HR+ breast cancer was significantly associated with improved recurrence-free survival (RFS) during the first 5 years (hazard ratio, 0.65; 95% CI, 0.56 to 0.77; < .001). Among patients treated with trastuzumab, cumulative hazard for RFS was lower in patients with HR+ HER2+ breast cancer during the first 5 years (10.96% 17.48%; hazard ratio, 0.60; 95% CI, 0.45 to 0.79; < .001). However, there was no significant difference in RFS based on HR status during years 5 to 10 (hazard ratio, 1.32; 95% CI, 0.93 to 1.88; = .12). A comparable degree of trastuzumab benefit was observed in HR+ and HR- breast cancers ( for interaction = .87). Furthermore, we observed low RoR in years 5 to 10 among patients with HR+ HER2+ breast cancer: 3.23% in patients without lymph node involvement (N0) and 6.39% in patients with involvement of one to three lymph nodes (N1). The benefit of adjuvant trastuzumab persists for a long time. A distinct pattern of recurrence was observed between HR+ and HR- HER2+ disease but with similar degree of benefit from adjuvant trastuzumab. RoR in years 5 to 10 in HR+ HER2+ breast cancer is low, particularly in patients with N0 or N1 disease.