Poorly differentiated adenocarcinomas of prostate versus high-grade urothelial carcinoma of the bladder: a diagnostic dilemma with immunohistochemical evaluation of 2 cases.

The differential diagnosis between carcinoma of the urinary bladder and adenocarcinoma of the prostate can be difficult, especially in the poorly differentiated forms infiltrating the neighboring organs. In this article, the authors report 2 cases that pose a diagnostic dilemma to the pathologist. The first is an infiltration of the bladder by a poorly differentiated adenocarcinoma of the prostate, which was clinically suspected as a papillary urothelial neoplasm. The second is a collision tumor composed of prostatic adenocarcinoma and urothelial carcinoma observed on a core needle biopsy of the prostate. In both cases, a large panel of immunohistochemical markers were used and demonstrated positivity for prostate-specific antigen and alpha methyl racemase in the prostatic carcinomas and immunoreactivity for CK7, CK20, Ag 34betaE12, and p53 in the urothelial carcinoma. The differentiating histological and immunohistochemical findings are discussed.