Recurrent prostate carcinoma presenting as omental large cell carcinoma with neuroendocrine differentiation and resulting in bowel obstruction.

Neuroendocrine differentiation in the neoplastic prostate varies from foci of adenocarcinoma showing immunoreactivity to the pure small cell carcinoma, which correlates with poor prognosis. Widely metastatic disease in unusual sites is reported for small cell carcinoma, and rarely is the serum prostate-specific antigen level elevated. We report a case of recurrent prostate adenocarcinoma presenting as bowel obstruction due to widespread metastatic disease in the omentum and peritoneum. The histopathology of the omental metastasis was that of a large cell neuroendocrine carcinoma, without evidence of an adenocarcinoma. The absence of a clinically evident second primary tumor, the concomitant elevated serum prostate-specific antigen level, and the positive tissue immunoreactivities to prostatic markers all supported the prostatic origin of the omental tumor. Review of the importance of prostatic neuroendocrine differentiation and its unusual metastatic patterns is presented.