Gastrointestinal neuroendocrine cell proliferations.

The gastrointestinal neuroendocrine cell proliferations are comprised of a few hyperplasias and various neoplasias. The better characterized hyperplasias include G-cell hyperplasia, either primary or secondary, enterochromaffin-like (ECL)-cell hyperplasias, generally secondary to hypergastrinemia, and EC-cell hyperplasias. The neoplasias include carcinoid tumors, demonstrating low malignancy and divided into foregut, midgut, and hindgut varieties, poorly differentiated neuroendocrine carcinomas resembling their pulmonary counterparts the "oat cell" carcinomas both in histological pattern and in their highly malignant behavior mixed endo-exocrine tumors, which in turn can be divided into composite tumors formed by a population of endocrine cells and a population of exocrine cells, and amphicrine tumors formed by a uniform population of cells with a mixture of endocrine and exocrine phenotypic traits. Although some of these mixed tumors show a degree of malignancy intermediate between the classical carcinoid and an adenocarcinoma, more information must be gathered to establish firm prognostic parameters for these relatively new entities.