Small cell carcinoma of the prostate expressing prostate-specific antigen and showing syndrome of inappropriate secretion of antidiuretic hormone: an autopsy case report.

An autopsy case of primary small cell carcinoma (SCC) of the prostate in a 68-year-old man is reported. The patient was admitted to hospital because of a bloody stool and suspected rectal cancer. However, a diagnosis of prostate cancer was made on the basis of a digital rectal examination, the serum level of prostate-specific antigen, and a needle biopsy of the prostate. The patient also experienced a syndrome of inappropriate secretion of antidiuretic hormone. He died 29 days after admission. At autopsy, the tumor had invaded the rectum, bladder and pelvic peritoneum. Metastases to the heart, vertebrae and lymph nodes were observed. Microscopically, the tumor was composed of small round cells that showed a solid growth pattern. Rosette formations were observed. Immunohistochemically, the tumor cells were positive for a prostatic epithelial marker and neuroendocrine markers. A high level of antidiuretic hormone was detected in the tumor tissue. To our knowledge, this is the first reported case of SCC of the prostate in which both a prostatic epithelial marker and neuroendocrine markers have been found in the same tumor. This finding supports the hypothesis that SCC of the prostate originates from a multipotential stem cell of the prostatic epithelium.