Rare prostatic carcinomas: histogenesis and morphologic pattern.

Most prostate cancers (90%) are acinar adenocarcinomas, originating in the peripheral or other prostatic regions. In a series of 650 cases of prostate carcinoma we found 7 cases of prostate carcinoma with unusual features, including 3 pure duct papillary carcinomas, 1 pure transitional cell carcinoma, 1 mucinous adenocarcinoma and 2 pure small cell carcinomas. Ductal papillary carcinoma consists of papillary fronds and branching, fibro-connective tissue, covered by a single layered to multilayered lining of columnar cells. Also the tumours located in central portions of the prostate derive from periurethral prostatic ducts. Primary transitional cell carcinoma of the prostate implies no pre-existing bladder cancer and arises from indifferent or reserve cells, lying between the luminal epithelium and the basement membrane of the periurethral ducts. The diagnosis of mucinous carcinoma should be reserved for these cases in which a sufficient quantity of extracellular mucin is seen to form pools and lakes. True mucinous carcinoma is likely to be a variant of prostate carcinoma. Classic oat cell carcinomas are composed of small, fairly uniform tumour cells only slightly larger than lymphocytes, arranged in solid nests wherein central necrosis is commonly observed. The pathological finding, clinical course and immunohistochemical studies, indicate that the small cell carcinoma of the prostate is most likely to be a neuroendocrine neoplasm.