ERBB2 and breast cancer: Hormone receptor‐positive (HR+)/human epidermal growth factor receptor 2‐positive (HER2+) breast cancer exhibits considerable heterogeneity, and it is of great interest whether patients with premenopausal HR+/HER2+ breast cancer treated with trastuzumab can benefit from ovarian function suppression (OFS) therapy similarly to HR+/HER2‐ breast cancer.