MICROGLANDULAR CARCINOMA OF THE PANCREAS - IMMUNOHISTOCHEMICAL AND ULTRASTRUCTURAL-STUDY OF AN UNUSUAL VARIANT OF PANCREATIC-CARCINOMA THATMAY CLOSELY RESEMBLE A NEUROENDOCRINE NEOPLASM

Two cases are described of an unusual form of primary adenocarcinoma o f the pancreas characterized histologically by their striking resembla nce with a neuroendocrine neoplasm. The tumors were composed of a popu lation of relatively small, uniform cells arranged in sheets admixed w ith small microglandular structures resulting in a cribriform pattern of growth. The tumor cells displayed scant cytoplasm with indistinct c ell borders and round to oval nuclei with irregular clumping of chroma tin and small, inconspicuous nucleoli. Immunohistochemical studies in both cases showed positivity of the neoplastic cells with CAM 5.2 anti bodies and negative staining with a battery of neuroendocrine-related markers including chromogranin, NSE and synaptophysin, as well as with a variety of peptide hormones including insulin, glucagon, vasoactive intestinal polypeptide, gastrin and serotonin. Ultrastructural examin ation revealed a cohesive population of cells forming abortive glandul ar lumens lined by imperfectly formed microvilli and showing well-deve loped junctional complexes. No dense core neurosecretory granules or z ymogen granules could be identified in any of the cells, supporting a ductal type of differentiation for these tumors. The main importance o f recognizing this rare variant of pancreatic adenocarcinoma lies in a voiding misdiagnosis with other primary and metastatic neuroendocrine neoplasms of this organ. Immunohistochemical and ultrastructural exami nation will be of value in such cases for differential diagnosis.