Notably, druggable aberrations, such as FGFR2 fusions (9–15% in intrahepatic cholangiocarcinoma [iCCA]), IDH1 mutations (10–20%), HER2 overexpression or amplification (5–20% in cholangiocarcinoma [CCA] and 15–30% in gallbladder cancer [GBCa]), are observed with variable frequencies across biliary tract cancers. The gene discussed is ERBB2; the disease is biliary tract cancer.