Differential Effectiveness of Adjuvant Endocrine Therapy According to Menopausal Status, Body Mass Index, and Molecular Subtype in Hormone Receptor-Positive Breast Cancer.

The effectiveness of adjuvant endocrine therapy for hormone receptor-positive (HR+) breast cancer (BC) varies according to menopausal status, body mass index (BMI), and tumor biology. We evaluated the association between selective estrogen receptor modulators (SERMs), aromatase inhibitors (AIs), and BC-specific mortality according to menopausal status, BMI, and molecular subtype in a nationwide Korean cohort. We analyzed data from 31,030 patients with HR+ BC who were registered in the Korean Breast Cancer Society Registry, diagnosed between 2000 and 2008, and followed through 2013. Cox proportional hazards models were used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for BC-specific mortality after adjusting for demographic and clinical factors. Of the 31,030 patients, 19,634 received SERM therapy, and 3,354 received AI therapy. SERM use was associated with lower BC-specific mortality in premenopausal women (HR, 0.75; 95% CI, 0.63-0.91), whereas AI therapy was more strongly associated with lower BC-specific mortality among postmenopausal women (HR, 0.76; 95% CI, 0.61-0.94). Lower BC-specific mortality was observed among patients with a BMI ≥ 23 kg/m² who received SERM (HR, 0.84; 95% CI, 0.72-0.98) or AI therapy (HR, 0.78; 95% CI, 0.62-0.99). The strongest association with lower BC-specific mortality was observed in postmenopausal women with luminal B tumors (HR, 0.59; 95% CI, 0.42-0.83). The association between adjuvant endocrine therapy and BC-specific mortality differed according to menopausal status, BMI, and molecular subtype. These findings suggest that menopausal status, BMI, and molecular subtype are important considerations when evaluating endocrine treatment strategies.