ERBB2 and biliary tract neoplasm: In a previous study, biliary tract cancers were classified according to druggable genes—FGFR (FGFR pathway alterations or FGFR2 fusion/rearrangement), HER2 (ERBB2 amplification and mutations), IDH1 (IDH1 alterations), BRAF (BRAF alterations), MSI (MSI-H or MSI-deficient mismatch repair), NTRK (NTRK fusion/rearrangement), and others [29].