Answer: Ductal adenocarcinoma of the prostate

Histology: Sections show delicate papillary fronds that are covered bland stratified epithelium. The fronds have fibrovascular cores and are lined by cuboidal-columnar cells that are overlapping and have hyperchromatic oval nuclei some with small nucleoli. No umbrella cells are noted. The neoplastic cells appear to be glandular and resemble prostatic acinar epithelium. Immunostains demonstrate that the lining cells are strongly and diffusely positive for prostatic markers (PSA, p501s and PSMA).

Discussion: Centrally located adenocarcinomas of the prostate can present as a single urethral polyp that grossly mimics a benign urothelial polyp. Histologically, prostatic ductal adenocarcinomas are composed of variably atypical cuboidal-columnar cells that usually have hyperchromatic nuclei with or without prominent nucleoli and are arranged in a cribriform, solid or papillary pattern. Residual urothelial cells may also be present. The histologic diagnosis can be difficult in cases where the tumor cells exhibit minimal atypia and no prostatic adenocarcinoma is suspected clinically. Immunohistochemistry for prostatic markers is typically positive in prostatic ductal adenocarcinoma and thus can be very helpful in making the diagnosis. These tumors are analogous in their behavior to acinar adenocarcinoma, Gleason score 4+4=8.