Endocrine Therapy in Premenopausal Hormone Receptor–Positive Breast Cancer

Systemic therapy for premenopausal women with hormone receptor–positive breast cancer has evolved in the last 5 years, but critical questions remain. Recent randomized trials have demonstrated a benefit for the addition of ovarian suppression to endocrine therapy in patients with breast cancers considered to be at high risk for recurrence, whereas those with lower-risk cancers seem to have a favorable outcome with tamoxifen alone. Two large randomized trials have demonstrated a benefit for extending adjuvant tamoxifen beyond 5 years. Currently the choice of systemic therapy is selected empirically but molecular profiling may, in the near future, provide a more conclusive means of selecting an endocrine therapeutic approach for premenopausal patients. Given that a significant subset of hormone receptor–positive cancers are intrinsically resistant to endocrine agents, as well as the finding that inhibiting cyclin-dependent kinases 4 and 6 and mammalian target of rapamycin appears to potentially reverse this resistance in patients with metastatic disease, evaluation of these agents in the early-stage setting is ongoing.