Primitive neuroectodermal tumors of the pancreas: a report of seven cases of a rare neoplasm.

Primitive neuroectodermal tumors (PNETs) have rarely been described in solid organs. We report a series of seven PNETs of the pancreas. The clinical, gross, microscopic, and immunohistochemical features of these seven PNETs of the pancreas are described, as are the genetic analyses in five cases. The patients ranged in age from 6 to 25 years (mean 18 years). Four of the patients were male. All of the patients presented with jaundice and/or abdominal pain. All of the tumors were located in the head of the pancreas, and they ranged in size from 3.5 to 9.0 cm. Light microscopy revealed the typical morphologic features of PNETs. By immunohistochemistry the neoplastic cells in all seven cases expressed O13 (CD99, p30/32MIC2). In five of six tested cases, the neoplastic cells also expressed cytokeratin. All of the tumors expressed neural-neuroendocrine markers. Two of the three cases examined ultrastructurally showed prominent epithelial features. There was cytogenetic or molecular genetic evidence of the t(11;22)(q24;q12) in four of five cases examined. Clinical follow-up was available in five cases. Two of the patients were alive with no evidence of disease at 33 and 43 months. One patient was alive with disease at 27 months. One patient died of postoperative complications. Another patient died of disease 4 years after diagnosis. PNET can sometimes arise as a primary neoplasm of the pancreas. Like PNETs arising in more conventional sites, pancreatic PNETs occur in the pediatric and adolescent population, show the characteristic staining with O13, and typically harbor the t(11;22)(q24;q12) chromosomal translocation. PNETs should be included in the differential diagnosis of poorly differentiated small round cell tumors of the pancreas. Moreover, they should not be confused with pancreatic endocrine tumors, which also demonstrate dual epithelial and neuroendocrine differentiation by immunohistochemistry and express O13 in 30% of cases.