PAX8 is expressed in pancreatic well-differentiated neuroendocrine tumors and in extrapancreatic poorly differentiated neuroendocrine carcinomas in fine-needle aspiration biopsy specimens.

Neuroendocrine Tumors

Tumors whose cells possess secretory granules and originate from the neuroectoderm, i.e., the cells of the ectoblast or epiblast that program the neuroendocrine system. Common properties across most neuroendocrine tumors include ectopic hormone production (often via APUD CELLS), the presence of tumor-associated antigens, and isozyme composition.

Carcinoma, Neuroendocrine

A group of carcinomas which share a characteristic morphology, often being composed of clusters and trabecular sheets of round "blue cells", granular chromatin, and an attenuated rim of poorly demarcated cytoplasm. Neuroendocrine tumors include carcinoids, small ("oat") cell carcinomas, medullary carcinoma of the thyroid, Merkel cell tumor, cutaneous neuroendocrine carcinoma, pancreatic islet cell tumors, and pheochromocytoma. Neurosecretory granules are found within the tumor cells. (Segen, Dictionary of Modern Medicine, 1992)

Synaptophysin

A 38-kDa integral membrane glycoprotein of the presynaptic vesicles in neuron and neuroendocrine cells. It is expressed by a variety of normal and neoplastic neuroendocrine cells and is therefore used as an immunocytochemical marker for neuroendocrine differentiation in various tumors. In ALZHEIMER DISEASE and other dementing disorders, there is an important synapse loss due in part to a decrease of synaptophysin in the presynaptic vesicles.

Pancreatic Neoplasms

Tumors or cancer of the PANCREAS. Depending on the types of ISLET CELLS present in the tumors, various hormones can be secreted: GLUCAGON from PANCREATIC ALPHA CELLS; INSULIN from PANCREATIC BETA CELLS; and SOMATOSTATIN from the SOMATOSTATIN-SECRETING CELLS. Most are malignant except the insulin-producing tumors (INSULINOMA).

Vipoma

A tumor that secretes VASOACTIVE INTESTINAL PEPTIDE, a neuropeptide that causes VASODILATION; relaxation of smooth muscles; watery DIARRHEA; HYPOKALEMIA; and HYPOCHLORHYDRIA. Vipomas, derived from the pancreatic ISLET CELLS, generally are malignant and can secrete other hormones. In most cases, Vipomas are located in the PANCREAS but can be found in extrapancreatic sites.