Primary small cell neuroendocrine carcinoma of the kidney.

The histological, immunohistochemical, and ultrastructural features of a primary small cell neuroendocrine carcinoma of the renal parenchyma are described. Tumor cells were positive for cytokeratin, neuron-specific enolase, and Leu 7, but Grimelius- and chromogranin-negative. They also exhibited positivity with anti-MIC2 antibody. By electron microscopy, tonofibrils, primitive desmosomes, and dense-core granules with a neuroendocrine appearance were present. This is only the 7th recorded example of such a tumor at this site, which showed an aggressive course characterized by widespread bony metastases.