Mixed acinar–endocrine carcinoma of the pancreas. A clinicopathological study and comparison with acinar-cell carcinoma

We compared the clinicopathological features of acinar-cell carcinomas (ACCs) with those of mixed acinar–endocrine carcinomas (MAECs). Specimens from 37 patients with ACC and 6 patients with MAEC were examined histologically and immunohistochemically. The mean age of ACC and MAEC patients was similar (61.3 years versus 58.4 years), but the sex ratio differed (ACC, 29 males and 8 females; MAEC, 2 males and 4 females). The size of the tumor was large in both cases (ACC, 13.8 cm in diameter; MAEC, 8.2 cm). Immunohistochemically, more than half of the tumor cells in all tumors, whether ACC or MAEC, stained for trypsin. In 20 of the 37 ACCs (54%), scattered endocrine cells (SECs) were found, which stained positively for synaptophysin (SYN) and/or chromogranin A (CGA). Interestingly, there was also a difference in the sex ratio between ACC patients without SECs (16 males and 1 female) and ACC patients with SECs (13 males and 7 females). In MAECs, the cells staining for SYN were more common than those staining for CGA and made up more than one-third of the neoplastic-cell population. In all but one case (in which the endocrine component was arranged in islet-like cell clusters), the endocrine cells were intimately mixed with trypsin-positive tumor cells. The endocrine cells only rarely expressed one of the known pancreatic or gastrointestinal hormones. Both ACCs and MAECs had a high proliferation rate and lacked p53 overexpression or progesterone and estrogen receptors. This study revealed that ACCS and MAECs share most clinicopathological features and, therefore, may form a single tumor entity, though they differ in the number of endocrine cells. The frequent identification of endocrine cells in these tumors suggests the existence of a pluripotent cell of origin that is capable of differentiating into acinar and endocrine cells.