Adjuvant endocrine therapy for premenopausal women with hormone-responsive breast cancer

Multiple strategies for endocrine treatment of premenopausal women with hormone-responsive breast cancer have been assessed and results have been presented over the last two years. These include tamoxifen for 5-10 years (ATLAS and aTTom), tamoxifen for 5 years followed by aromatase inhibitor (AI) for 5 years for women who have become postmenopausal (MA-17); ovarian ablation (OA) by surgery (EBCTCG overview); ovarian function suppression (OFS) by LHRH agonist (LHRH agonist meta-analysis); or combinations of approaches including OFS plus tamoxifen or AI (SOFT, TEXT, ABCSG 12 and E3193). Many of these trials have taken place in the backdrop of (neo)adjuvant chemotherapy which can confound interpretation because such therapy can suppress ovarian function either transiently or permanently. Nonetheless these trials suggest in aggregate that 10 years of tamoxifen are better than 5 years and that a program of extended adjuvant therapy of tamoxifen for 5 years followed by aromatase inhibitor for 5 years is effective for suitable candidates. The SOFT and E3193 trials do not show a major advantage for use of OFS + tamoxifen compared to tamoxifen alone. The joint SOFT/TEXT analysis and ABCGS12 trials both suggest that outcomes can be excellent with the use of combined endocrine therapy alone in properly selected patients but give conflicting results with regard to potential benefits for OFS + AI compared with OFS + tamoxifen. Further work will be needed to ascertain long-term outcomes, identify factors that predict who will benefit from extended adjuvant endocrine therapy, and assess role of OFS by medical or surgical means. It is clear, however, that endocrine therapy is a critical part of the adjuvant regimen for most premenopausal women with hormone-responsive breast cancer, and a subset of these women with luminal A-type tumors can be safely treated with endocrine therapy alone.