Malignant neuroendocrine tumor of the jejunum with osteoclast-like giant cells. Enzyme histochemistry distinguishes tumor cells from giant cells.

We report a case of a neuroendocrine tumor of the jejunum metastatic to the liver in a 26-year-old woman. Light and electron microscopy of this tumor revealed a poorly differentiated neoplasm composed of clusters of round to polygonal cells compatible with a diagnosis of neuroendocrine tumor. In the absence of identifiable silver-staining granules or immunocytochemical demonstration of a specific hormone product in tumor cells, this tumor cannot be further classified among the various neuroendocrine tumors that may arise in this location. However, interspersed among tumor cells was a distinct population of multinucleate giant cells having an appearance similar to benign osteoclasts. Enzyme histochemistry for 5'-nucleotidase, acid phosphatase, and nonspecific esterase each showed a dichotomous staining pattern for the small tumor cells and giant cells and suggest that the giant cells are not tumor derived, but represent a second, presumably reactive, cell population.