SMAD4 and biliary tract cancer: According to their report, common mutations in biliary tract cancers, including gallbladder cancer, were detected in TP53, BRCA1, BRCA2, and PIK3CA; intrahepatic and extrahepatic duct-shared mutations were detected in KRAS, SMAD4, ARID1A, and GNAS; intrahepatic duct-specific mutations were detected in FGFR2 fusion, IDH1/2, EPHA2, and BAP1 genes; and extrahepatic duct-specific mutations were detected in PRKACA/PRKACB fusion, ELF3, and ARID1B genes.