ERBB2 and cholangiocarcinoma: Overexpression of HER2 has been found in a variety of solid tumors, such as breast cancer, stomach cancer, cholangiocarcinoma, colorectal cancer, non-small cell lung cancer, endometrial cancer, and bladder cancer, with positive rates ranging from more than 50% in endometrial cancer to 2% in non-small cell lung cancer, but there is significant inter-tumor heterogeneity in HER2 overexpression patterns (38, 39).