Signet ring cell carcinoma of prostate. Immunohistochemical and ultrastructural study of a case.

Signet ring cell adenocarcinoma (SRCA) is an extremely rare tumor of the prostate. We document with histochemistry, immunohistochemistry, and electron microscopy an incidental "signet ring" cell adenocarcinoma of the prostate in a fifty-seven-year-old white male with chronic lymphocytic leukemia who died of an intracerebral hemorrhage. The signet ring cells stained weakly for neutral mucin and were strongly positive for both prostate-specific antigen and prostate acid phosphatase. In addition, electron microscopy demonstrated intracellular lumina with microvilli and cytoplasmic vacuoles of mucin. This case conclusively supports the existence of SRCA of the prostate.