ERBB2 and breast cancer: HER2 is implicated in 15–20% of breast cancers [1], 15–20% of gastroesophageal adenocarcinomas [2], 8–66% of ovarian cancers [3], 17–80% of endometrial cancers [3], 6–17% of bladder cancers [4], 2–4% of lung cancers [5], 3–5% of colon cancer [6], and 50% of head and neck cancers [7].