De-escalated chemotherapy and endocrine therapy outcomes in young women with stage I HR+/HER2+ breast cancer: An international real-world study

Background: Use of taxane-only chemotherapy for stage I HR+/HER2+ breast cancer has increased, potentially preserving ovarian function and shifting endocrine therapy (ET) strategies. Outcomes in premenopausal women were not defined. Methods: Patients ≤45 years with stage I HR+/HER2+ breast cancer were identified from a multicenter registry. IDFS was assessed by chemotherapy and ET. Results: Thirteen IDFS events (4 distant) occurred among 244 patients. Six-year IDFS was 95.5% (multiagent chemotherapy) and 94.1% (taxane-only) (p = 0.56), and 95.9%, 93.8%, and 96.9% with tamoxifen, tamoxifen + OFS, and AI + OFS (p = 0.56). Conclusions: Outcomes were excellent regardless of chemotherapy or ET, suggesting limited incremental benefit from treatment intensification.