ERBB2 and cholangiocarcinoma: There is currently no description of HER2 gene amplification/overexpression subtype mutation characteristics in cholangiocarcinoma; however, research in colorectal cancer has found that all HER2-amplified tumors lacked activating mutations of MAPK pathway genes (including KRAS, NRAS, and BRAF) except for two tumors with KRAS mutations.