OBJECTIVETo study the histogenesis, pathologic features and differential diagnosis of prostatic primary signet ring cell carcinoma.

METHODS10 cases of the primary signet ring cell carcinoma were detected from 262 cases of prostate carcinomas diagnosed on needle biopsy were investigated by routine pathological, immunohistochemical and histochemical methods, and then compared with 10 cases of signet ring cell carcinomas of the stomach and colon. 3 cases were studied with electron microscopy.

RESULTS9 cases of prostate signet ring cell carcinoma were associated with concurrent high-grade conventional prostatic carcinoma, but at least 25% of the neoplasm consisted of signet ring cells. Only one case was pure signet ring cell carcinoma. Neoplastic signet ring cells may be divided into two types: the first type showed formation of intracytoplasmic lumina or vacuole, and the second type had intracytoplasmic accumulation of excess PSA and/or PAP. Both types of signet ring cells were negative for mucin staining (AB/PAS and mucicarmine). Therefore they differed from signet ring cell carcinomas of the stomach and colon.

CONCLUSIONSPrimary prostate signet ring cell carcinoma is a low-differentiated adenocarcinoma of a special histologic type, which arises from the epithelial cells of the prostate acinus. They can be distinguished from metastatic signet ring cell carcinoma of the stomach and colon and also from vacuolate degeneration of conventional carcinoma after endocrine or radiation therapy.