Where and when does pancreatic carcinoma start?

The phenotypic classification of pancreatic neoplasms is based on their cellular lineage. Thus, tumors with a ductal, acinar and endocrine phenotype can be distinguished. Most pancreatic neoplasms show a ductal phenotype and can be classified as ductal adenocarcinomas. Less common tumors with a ductal phenotype are the variants of ductal adenocarcinoma, intraductal papillary-mucinous neoplasm (including colloid carcinoma), mucinous cystic neoplasm, medullary carcinoma and other rare tumors. Ductal adenocarcinomas most likely develop on the basis of ductal proliferative lesions arising in the pancreatic duct system. A recently adopted classification system for these lesions distinguishes between three grades of pancreatic intraepithelial neoplasia (PanIN). Molecular studies revealed that PanIN-2 and PanIN-3 lesions represent a distinct step toward invasive carcinoma.