Adjuvant Therapy in Breast Cancer Patients With Microscopic Residual Disease.

INTRODUCTION:Surgical resection is the gold standard for early-stage breast cancer. Positive surgical margins are associated with poor outcome. Endocrine therapy (ET) is recommended as primary systemic treatment for hormone receptor positive (HR+) breast cancer after surgery. We hypothesized that chemoenocrine therapy (CET) would not be associated with improved survival relative to ET for patients with positive margins. MATERIALS AND METHODS:The National Cancer Database was queried for pathologic stage I HR + HER2-breast cancer patients treated with partial mastectomy and adjuvant whole-breast irradiation between 2004 and 2017. The adjuvant treatment approaches to positive surgical margins were investigated and compared. Overall survival was compared between systemic treatment groups using multivariable cox proportional hazards regression. RESULTS:Among 228,453 patients, a positive surgical margin (microscopic residual disease, R1) was identified in 3561 (1.6%) patients. Compared with complete resections, positive margin was associated with inferior overall survival (hazard ratio [HR] = 1.276, P = 0.003). Among the R1 patients, 78.7% received ET only, 11.7% received CET, 1.2% received chemotherapy only, and 8.5% received no systemic therapy. After controlling for patient, facility, and tumor characteristics, ET provided greatest survival benefit (relative to no therapy, HR = 0.378, P < 0.001) followed by CET (HR = 0.446, P = 0.020). Compared with ET alone, CET is not associated with additional overall survival benefit (HR = 1.179, P = 0.595). CONCLUSIONS:CET appeared not to be associated with an improved overall survival in early stage HR + HER2-breast cancer with microscopic residual disease relative to ET. Positive surgical margins therefore are probably not a relevant clinical factor for adjuvant chemotherapy decision-making.