Small cell carcinoma of the genitourinary tract: an immunohistochemical, electron microscopic and clinicopathological study.

We examined 13 cases of small cell carcinoma of the genitourinary tract to evaluate and compare the immunocytochemical and ultrastructural features as well as the clinicopathological behavior. Immunohistochemical stains revealed that neuron specific enolase and chromogranin showed differences in staining between the bladder and prostate, as well as between the small cell and adenocarcinomatous components of the prostate. Also, synaptophysin was negative over-all in 12 of 13 cases. Epithelial membrane antigen, carcinoembryonic antigen and keratin showed strong focal positivity within the small cell component. Electron microscopy was performed in 4 cases, with 3 demonstrating neurosecretory granules. Clinically, 6 of the 7 patients with adenocarcinoma/small cell carcinoma of the prostate did poorly, all with a survival of 15 months or less. Of 5 patients with transitional cell/small cell carcinoma of the bladder 2 fared better (both had no evidence of disease at 12 months and 11 years, respectively). Based upon the immunostaining and electron microscopic findings, small cell carcinoma of the genitourinary tract is heterogeneous in appearance and, therefore, may arise from a multipotential cell of origin. This cell of origin may be organ-specific, as demonstrated by the variability in staining characteristics among the prostate, bladder and kidney, as well as by the differences in the clinical behavior of these malignancies. Small cell carcinoma of the prostate has a poor prognosis, while small cell carcinoma of the bladder may portend a better prognosis if diagnosed at an early stage.