Association of endocrine therapy with overall survival in women with hormone receptor-positive, HER2-negative, node-negative breast cancer of favorable histology.

Breast carcinomas are histologically diverse and have distinct prognostic significance. Early-stage breast cancers with favorable histopathologic features are managed comprehensively including adjuvant endocrine therapy at the discretion of clinicians. Using a de-identified large national cancer registry, we evaluated the overall survival benefit of endocrine therapy in patients diagnosed with HR-positive, HER2-negative, pT1-2N0 (tumor size < 3 cm), non-high-grade breast cancer with favorable histologies including tubular, mucinous, and cribriform types. On propensity score matching of 2482 matched pairs, the addition of adjuvant endocrine therapy was associated with improved OS (hazard ratio: 0.81; 95% CI: 0.67-0.98, P = .03). Our findings suggest a role for endocrine therapy in future risk mitigation for favorable histologies but should be balanced with the implications of prolonged utilization.