Pancreatic cancer secondary to biliary tract cancer associated with pancreaticobiliary maljunction: intraductal dissemination through the common channel.

Patients with pancreaticobiliary maljunction (PBM) have a high risk of biliary tract cancer (BTC). The risk of pancreatic cancer is also reported to be higher in patients with PBM compared to the general population; the underlying cause remains unclear. We report a 73-year-old man with widespread pancreatic cancer involving the entire pancreas. The patient previously underwent curative resection for gallbladder cancer and hilar cholangiocarcinoma concomitant with PBM. A total pancreatectomy was performed for the new pancreatic lesion. Histopathological examination revealed a papillary tumor predominantly composed of intraepithelial lesions that extended throughout the pancreatic duct, with skip lesions and irregular invasive foci at multiple sites within the duct. The morphological features and mucin profile were similar to those of the previous biliary lesions. Genetic analysis of the current lesion showed wild-type KRAS, GNAS, and PIK3CA genes consistent with the previous lesions, indicating that the pancreatic and biliary lesions were molecularly identical clones. Based on the clinicopathological findings and molecular analysis, we concluded that the BTC had spread intraluminally to the pancreatic duct through the common channel of the PBM, resulting in intraductal dissemination. Patients with PBM should be followed for pancreatic lesions, because of the risk of intraductal dissemination of BTC.