ERBB2 and endometrial serous adenocarcinoma: Human epidermal growth factor receptor 2 (HER2) overexpression plays a critical role in the development and progression of breast cancer, gastric cancer, and uterine serous carcinoma (USC) (1–3), and has been established as a standard therapeutic target in breast cancer and a subset of patients with HER2-positive advanced gastric cancer (4, 5).