'Endometrial' adenocarcinoma of the prostatic urethra arising in a villous polyp. A light microscopic and immunoperoxidase study.

A 77-year-old man had a papillary neoplasm of the prostatic urethra removed by transurethral resection. Light microscopically, much of the tissue consisted of a benign villous polyp lined by prostatic epithelium. An adenocarcinoma with cells that resembled those of uterine endometrial carcinoma was also present within the villous polyp. Using immunoperoxidase techniques, prostatic acid phosphatase and prostatic-specific antigen were localized in the epithelial cells of both the villous polyp and the adenocarcinoma. To our knowledge, this is the first reported case of adenocarcinoma arising in a urethral polyp. The immunohistochemical findings and the close association of the adenocarcinoma with the prostatic epithelium of the villous polyp provided evidence that so-called endometrial carcinoma of the prostatic utricle is of prostatic epithelial origin rather than müllerian derivation.