Medical Therapy for Hormone Receptor-Positive, HER2-Negative Stage I-III Breast Cancer: ASCO Living Guideline, Version 2026.1.0

PURPOSE: To provide recommendations on use of medical therapies for patients with stage I-III hormone receptor-positive, HER2-negative breast cancer. METHODS: An Expert Panel including patient representation completed a systematic review of the evidence and formulated recommendations for practice. Eligible studies included patients with stage I-III hormone receptor-positive, HER2-negative breast cancer and evaluated neoadjuvant or adjuvant chemotherapy, endocrine therapy, immunotherapy, or targeted therapy. Outcomes of interest included pathologic complete response, disease-free survival, distant recurrence-free survival, overall survival, health-related quality of life, and treatment-related adverse effects. RESULTS: Forty-five randomized clinical trials (68 references) published from 2018-2026 were identified by the broad literature search. Supplemental searches identified six individual patient data meta-analyses and 21 retrospective studies that, combined with the primary clinical trials, informed guidance on which patients should receive treatment, which treatments should be selected, optimal treatment timing, duration of treatment, and approaches to support adherence. A final section addresses estimation of prognosis and treatment benefit to inform decisions across all phases of treatment. RECOMMENDATIONS: The recommendations are organized to follow the longitudinal care of patients with stage I-III hormone receptor-positive, HER2-negative breast cancer, reflecting the sequence of decisions faced by clinicians from diagnosis through completion of systemic therapy. Endocrine therapy remains the foundation of treatment for stage I-III hormone receptor-positive, HER2-negative breast cancer. For selected patients, chemotherapy and targeted therapies can further reduce the risk of recurrence and breast cancer death. Treatment recommendations should integrate clinicopathologic features, genomic assays, patient preferences, treatment tolerability, and estimated recurrence risk. The guideline provides evidence-based recommendations to support individualized treatment selection and sequencing across the continuum of care.Additional information is available on the ASCO Publications website.