Over the past 5 decades, new therapies have substantially increased the median overall survival of patients with MBC from approximately 2 years to more than 5 years, depending on the molecular subtype of breast cancer, with greatest gains in hormone receptor (HR)–positive and human epidermal growth factor receptor 2 (ERBB2) overexpressing breast cancers.5,6,7 Collective strategy in the treatment of MBC is to sequence therapies until progression or unacceptable toxic effects; specific drugs depend on HR and ERBB2 status. This evidence concerns the gene ERBB2 and breast cancer.