WHO-classification 2000: exocrine pancreatic tumors.

The new WHO-classification is more than a histological description of the tumors of the exocrine pancreas. It is a clinicopathological overview that also covers the most recent genetic data on each tumor-type. New issues concern the possible ductal adenocarcinoma precursor lesions and the further characterization of pancreatic neoplasms showing a ductal phenotype. Pancreatic duct lesions have been discussed as tumor precursors. We will present the recently adopted standard system for these lesions, which distinguishes between three grades of pancreatic intraepithelial neoplasia (PanIN). Molecular studies revealed that PanIN-2 and PanIN-3 lesions represent a distinct step towards invasive carcinoma. Another focus of the review will be the advances that have been made in the further immunocytochemical and molecular characterization of special pancreatic neoplasms showing a ductal phenotype, such as undifferentiated carcinoma, mucinous noncystic (colloid) carcinoma, intraductal papillary mucinous neoplasm, mucinous cystic neoplasm, medullary carcinoma and other rare tumors.