Tumors of the pancreas,the ampulla of Vater,and the extrahepatic and intrahepatic bile ducts have significant histological similarities due to the common embryonic origin of the pancreatobiliary system.This obviates the need for discovery of biomarkers with diagnostic and prognostic value for these tumors.Mucins,especially MUC-1,-2,-4 and-5AC,are important candidates for developing into such reliable biomarkers.Increased expression of MUC1 occurs in pancreatic ductal adenocarcinomas and is associated with increased degrees of dysplasia in pancreatic intraepithelial neoplasia(Pan IN).Positive expression of MUC2 in intraductal papillary mucinus neoplasms(IPMN) of the intestinal type indicates high potential progression to invasive carcinoma with de novo expression of MUC1,while absence of MUC2 expression in IPMNs of gastric type implies low potential to malignant evolution.De novo MUC4 expression correlates to the severity of dysplasia in Pan IN and is associated with a poor prognosis in patients with pancreatic ductal adenocarcinomas.In biliary intraepithelial neoplasia(Bil IN),increased expression of MUC1 is associated with higher degrees of dysplasia.Intrahepatic cholangiocarcinomas(ICC) are characterized by increased expression of all glycoforms of MUC1.Positive MUC2 expression in intraductal papillary neoplasm of the bile ducts(IPNB) of the intestinal type indicates high malignant potential with de novo expression of MUC1 in the invasive element.Absent MUC2 expression in any degree of Bil IN may prove useful in differentiating them from IPNB.De novo expression of MUC4 is associated with poor prognosis in patients with ICC or carcinoma of the extrahepatic bile ducts(EHBDC).High de novo expression of MUC5 AC is found in all degrees of Bil IN and all types of IPNB and ICC.The MUC5 AC is useful in the detection of neoplastic lesions of the bile duct at an early stage.Increased expression of mucin MUC1 in carcinoma of the ampulla of Vater associated with unfavorable behavior of the tumor,such as lymph node metastasis,infiltration of the pancreas and duodenum,advanced TNM classification and worse prognosis.Patients withintra-ampullary papillary-tubular neoplasm(IAPN) of the pancreatobiliary immunophenotype did not show MUC2,while those of the intestinal immunophenotype are MUC2 positive.The expression of MUC4 is associated with poor prognosis in patients with carcinoma of the ampulla of Vater favoring metastasis and making them resistant to apoptosis.Moreover,it appears that MUC4 positivity correlates with recurrence of the tumor.Expression of MUC5 AC is associated with the invasive potential of the tumor. Tumors of the pancreas, the ampulla of Vater, and the extrahepatic and intrahepatic bile ducts have significant histological similarities due to the common embryonic origin of the pancreatobiliary system. This obviates the need for discovery of biomarkers with diagnostic and prognostic value for these tumors. Mucins , especially MUC-1, -2, -4 and-5AC, are important candidates for developing into reliable biomarkers. Increased expression of MUC1 occurs in pancreatic ductal adenocarcinomas and is associated with increased degrees of dysplasia in pancreatic intraepithelial neoplasia (Pan IN) .Positive expression of MUC2 in intraductal papillary mucinus neoplasms (IPMN) of the intestinal type indicates high potential progression to invasive carcinoma with de novo expression of MUC1, while absence of MUC2 expression in IPMNs of gastric type implies low potential to malignant evolution. De novo MUC4 expression correlates to the severity of dysplasia in Pan IN and is associated with a poor prognosis in patients with pancreatic ductal adenocarcinomas. In biliary intraepithelial neoplasia (Bil IN), increased expression of MUC1 is associated with higher degrees of dysplasia. Intrahepatic cholangiocarcinomas (ICC) are characterized by increased expression of all glycoforms of MUC1.Positive MUC2 expression in intraductal papillary neoplasm of the bile ducts (IPNB) of the intestinal type indicates high malignant potential with de novo expression of MUC1 in the invasive element. Absent MUC2 expression in any degree of Bil IN may prove useful in differentiating them from IPNB. De novo expression of MUC4 is associated with poor prognosis in patients with ICC or carcinoma of the extrahepatic bile ducts (EHBDC). High de novo expression of MUC5 AC is found in all degrees of Bil IN and all types of IPNB and ICC. MUC5 AC is useful in the detection of neoplastic lesions of the bile duct at an early stage. Increased expression of mucin MUC1 in carcinoma of the ampulla of Vater associated with unfavorable behavior of the tumor, such as lymph node metastasis, infiltration of the pancreas and duodenum, advanced TNM classification and worse prognosis. Patients with intra-ampullary papillary-tubular neoplasm (IAPN) of the pancreatobiliary immunophenotype did not show MUC2, while those of the intestinal immunophenotype are MUC2 positive. The expression of MUC4 is associated with poor prognosis in patients with carcinoma of the ampulla of Vater favoring metastasis and making it resistant to apoptosis. More over, it appears that MUC4 positivity correlates with recurrence of the tumor. Expression of MUC5 AC is associated with the invasive potential of the tumor.