ERBB2 and breast cancer: As of 2019, patients with hormone receptor–positive/human epidermal growth factor receptor 2–negative (HR+/HER2–), the most common BC subtype, who develop distant metastases (metastatic breast cancer [mBC]) have a 5‐year relative survival rate of only 35.4%, although improvements seem to have occurred post 2015 [2, 3, 4].