Mixed ductal-endocrine carcinomas of the pancreas and ductal adenocarcinomas with scattered endocrine cells: characterization of the endocrine cells.

We compared the histological and immunohistochemical features of mixed ductal-endocrine carcinomas of the pancreas with those of ductal adenocarcinomas (DACs) containing scattered tumor-associated endocrine cells (SECs). Three pancreatic neoplasms fulfilled the WHO criteria for mixed ductal-endocrine carcinomas. Two of them showed moderately to poorly differentiated glandular structures composed of both mucin producing and neuroendocrine cells. The third mixed ductal-endocrine carcinoma was of the composite type showing DAC structures and a solid component with small epithelial cells, most of them of neuroendocrine nature. In 32 of 34 cases of DAC located in the head (30 cases) and body to tail (4 cases) of the pancreas and showing lymph-node metastases, SECs were found, but they were few in number and irregularly distributed in the tumors. In three DACs a few SECs were also detected in lymph-node metastases. Double staining for chromogranin A and the proliferation marker Ki-S5 revealed that all SECs that were not intimately integrated into the neoplastic glandular epithelium failed to show proliferative activity and changes of the expression of tumor suppressor genes (p53 and DPC 4). These findings suggest that only those SECs that belong to the proliferative cell fraction may be of neoplastic origin, while the majority of SECs probably constitute a tumor-associated but non-neoplastic cell population. These features contrast with those of mixed ductal-endocrine carcinomas, in which all endocrine cells are a component of the neoplasm.