Problems in histological diagnosis of intraductal papillary-mucinous tumor (IPMT)

IPMTs (intraductal papillary-mucinous tumors) of the pancreas have been recognized as a distinct clinical entity. WHO used this term in most recent classification (1996). The present report reviews the WHO classification and recent descriptions of IPMT. Problems regarding the histological diagnosis and differential diagnosis are also discussed. In the WHO classification, IPMTs are classified into three categories: intraductal papillary-mucinous adenoma, intraductal papillary-mucinous tumor with moderate dysplasia and intraductal papillary-mucinous carcinoma. The classification is based on the tissue morphology, such as degree of dysplasia and pattern of proliferation. Some immunohistochemical and molecular markers have been reported for differential diagnosis and estimating the prognosis of IPMT. MUC1, Dpc-4, p53 and Ki-67. In making a differential diagnosis, mucinous cystic tumors are the most problematic. Communication with the pancreatic ducts, the presence of ovarian type stroma and capsular formation are key histological factors for a differential diagnosis between IPMTs and mucinous cystic tumors. The prognosis of IPMTs is favorable in general. However, once massive invasion has occurred, the prognosis is very poor, as in cases of ductal carcinoma. For further studies of IPMT, pathologists and clinicians involved in the diagnosis and treatment of IPMTs need to understand the concept of IPMTs and use the WHO classification.