Adjuvant endocrine treatment for estrogen receptor (ER)-positive/HER2-negative breast cancer

Approximately 70% of women with breast cancer worldwide receive a diagnosis of ER-positive/HER2-negative disease. Recurrence-free survival of the node-negative population of these women is approximately 85%, and most are treated with endocrine chemotherapy. Endocrine treatment for ER-positive/HER2-negative early breast cancer is a major treatment strategy. Breast cancer clinicians have gained much experience with this issue, but new data regarding adjuvant endocrine therapy have recently been accumulated. In the integrated analyses of the Suppression of Ovarian Function Trial (SOFT) and Tamoxifen and Exemestane Trial (TEXT) trials, the addition of ovarian function suppression (OFS) to tamoxifen showed a significant improvement in both 8-year disease-free survival [hazard ratio (HR) 0.76, 95% confidence interval (CI): 0.62-0.93] and overall survival (HR 0.67, 95% CI: 0.48-0.92) compared with tamoxifen alone for premenopausal patients with breast cancer, with the assumption of 5 years as an appropriate duration for OFS. The ATLAS trial showed that, compared with 5 years of tamoxifen, 10 years of tamoxifen provided further benefit to women with HR-positive early breast cancer in recurrence [5-9 years: Rate ratio (RR) 0.90, 95% CI: 0.79-1.07; ≥10 years: RR 0.75, 95% CI: 0.62-0.90; and all years: Log-rank P=0.002] and breast cancer mortality (5-9 years: RR 0.97, 95% CI: 0.79-1.18; ≥10 years: RR 0.71, 95% CI: 0.58-0.88; and all years: Log-rank P=0.01), particularly after reaching 10 years, which is considered a "carry over" benefit. In this review, adjuvant endocrine treatment for ER-positive/HER2-negative early breast cancer is discussed. Particular areas of focus are premenopausal patients, especially regarding the addition of OFS, postmenopausal patients, the duration of adjuvant endocrine therapy, the treatment implications of multigene expression assays, and adjuvant endocrine therapy for ductal carcinoma in situ. Some of this evidence supports the clinical management of breast cancer patients as well as clinical studies in the future.