ERBB2 and breast cancer: According to Surveillance, Epidemiology, and End Results (SEER) registries, among patients with known hormone receptor (HR)/human epidermal growth factor receptor 2 (HER2) status in 2010, 36,810 (72.7%) were found to be HR+/HER2–, which is the most frequently diagnosed molecular subtype among all breast cancer types (7).