Endocrine Therapy for Hormone Receptor–Positive Metastatic Breast Cancer: American Society of Clinical Oncology Guideline

Sequential hormone therapy is the preferential treatment for most women with HR-positive MBC. Except in cases of immediately life-threatening disease, hormone therapy, alone or in combination, should be used as initial treatment. Patients whose tumors express any level of hormone receptors should be offered hormone therapy. Treatment recommendations should be based on type of adjuvant treatment, disease-free interval, and organ function. Tumor markers should not be the sole criteria for determining tumor progression; use of additional biomarkers remains experimental. Assessment of menopausal status is critical; ovarian suppression or ablation should be included in premenopausal women. For postmenopausal women, aromatase inhibitors (AIs) are the preferred first-line endocrine therapy, with or without the cyclin-dependent kinase inhibitor palbociclib. As second-line therapy, fulvestrant should be administered at 500 mg with a loading schedule and may be administered with palbociclib. The mammalian target of rapamycin inhibitor everolimus may be administered with exemestane to postmenopausal women with MBC whose disease progresses while receiving nonsteroidal AIs. Among patients with HR-positive, human epidermal growth factor receptor 2-positive MBC, human epidermal growth factor receptor 2-targeted therapy plus an AI can be effective for those who are not chemotherapy candidates.