Small cell carcinoma of the prostate. II. Immunohistochemical and electron microscopic studies of 18 cases

To evaluate the histogenesis of small cell carcinoma of the prostate, 18 cases of this tumor (9 pure small cell and 9 combined adeno- and small cell carcinoma) were studied using immunohistochemical methods. Seven of the small cell components also were assessed by electron microscopic examination. Using neuron-specific enolase (NSE), prostatic acid phosphatase (PAP), and prostate-specific antigen (PSA) on tissue sections, three distinctive immunostaining patterns of small cell carcinoma components were identified: staining positive for NSE and negative for PSA and PAP (10 cases), staining positive for PSA and PAP and negative for NSE (3 cases), and negative reaction for all three antigens (5 cases). Electron microscopic study demonstrated neurosecretory granules in two cases. Based on the immunostaining and electron microscopic findings, small cell carcinomas of the prostate appear to be a heterogeneous group of tumors. Some of them are neuroendocrine carcinomas whereas others are poorly differentiated adenocarcinomas or, possibly, reserve cell carcinomas. Differences in immunostaining patterns or presence and absence of adenocarcinoma component do not reflect any differences in the uniformly poor prognosis of small cell carcinomas, in which median survival is 7.7 months. The authors believe that, because of such heterogeneity, small cell carcinomas of the prostate arise from multipotential prostatic epithelium and that an origin from specific neuroendocrine cells need not be implicated.