Pathologic classification of "pancreatic cancers": current concepts and challenges.

As the most common and most important cancer of the pancreas, with rapid mortality and now also as the third leading cause of cancer-related deaths in the United States, pancreatic ductal adenocarcinoma (PDAC) has become synonymous with "pancreas cancer". PDAC is also the prototype of the "pancreatobiliary-type" adenocarcinomas, along the biliary tract, ampullary and gallbladder cancers with the similar morphology and behavior. Recent molecular profiling studies have identified distinct subsets of PDAC, potentially with different behaviors and targetability. Moreover, while PDAC is by far the most common cancer of the pancreas, there are various other types that occur in this organ and are erroneously classified together with PDAC. Many of these have different molecular and biologic characteristics that warrant their management separately although they are also technically "pancreatic cancers". While some are closely related to PDAC and have as aggressive behavior (such as adenosquamous carcinomas which are recently recognized under "basal" like category in profiling studies, which are actually even worse prognostically than PDACs), in the meantime, others such as colloid carcinoma has a much better behavior than PDAC, and as a carcinoma with intestinal lineage (MUC2/CDX2) colloid carcinoma may require an entirely different treatment approach as well. Similarly, medullary carcinomas also appear to have different biology. Additionally, non-ductal cancers such as acinar, neuroendocrine, solid-pseudopapillary neoplasms and pancreatoblastoma have their respective clinicopathologic and molecular associations and warrant careful elimination in the management and study protocols. Another very problematic aspect in the classification of "pancreas cancer" is its delineation from the cancers of neighboring organs, in particular, ampullary/duodenal and common bile duct (CBD) cancers, for which recently more refined criteria have been provided. Additionally, the possibility of metastasis from another site and lymphomas also need to be considered. In summary, there is a whole host of cancers that occur in the pancreas that ought to be considered carefully before a case is classified as an ordinary "pancreas cancer" (PDAC).