ERBB2 and metastatic neoplasm: We sought to understand the endocrine sensitivity of patients with HR+/HER2- BrM and determine the associated risk of leptomeningeal metastatic disease (LMD).<h4>Methods</h4>We conducted a retrospective cohort study of 204 consecutive patients (≥18 yr of age) with HR+/HER- mBC who were treated for BrM at the Sunnybrook Odette Cancer Centre between 2008 and 2018.