Real-World Treatment Patterns and Outcomes in HER2-Altered Metastatic Breast Cancer Patients in the United States

This study aims to address the following key objectives in patients with HER2-altered mBC: Primary objectives * Estimate the prevalence of human epidermal growth factor receptor 2 positive (HER2+), human epidermal growth factor receptor 2 (HER2) mutation, cooccurrence of HER2+ and HER2 mutation among adult patients with metastatic breast cancer (mBC) * Among mBC patients with HER2+ and HER2 mutation, describe the following: * Baseline demographic and clinical characteristics * Treatment patterns during follow-up including 1L through fifth-line (5L) settings * Real-world overall survival (rwOS) for 1L through 5L Secondary objectives \- Among mBC patients with HER2+ and HER2 mutation, examine the following (as permissible in the study data): * Real-world progression-free survival (rwPFS) * Real-world time to discontinuation (rwTTD) * Real-world time to next treatment (rwTTNT) * Real-world overall response rate (rwORR)