SMAD4 and biliary tract neoplasm: Mutations of the Smad4 gene in other tumor types are less frequent, with a 16% rate in biliary tract cancers, 13% in colorectal carcinomas, 12% in breast cancers, bladder cancers and ovarian cancers, 7% in lung cancers, 6% in hepatocellular carcinoma and 4% in cervical cancers [14].