Answer: Prostatic duct adenocarcinoma

Histology: The lesion consists of a papillary mass within the prostatic urethra. The papillae are lined by glandular cells, which range from a single layer to being pseudo-stratified. In areas, tall columnar epithelium can be seen. The cells have abundant eosinophilic cytoplasm. The nuclei show significant atypia and are enlarged with prominent nucleoli.

Discussion: Prostatic duct adenocarcinoma can be differentiated from high-grade prostatic intraepithelial neoplasia by its architectural complexity, growth along true fibrovascular cores, and the degree of nuclear atypia. In this particular case, the entire tumor shows a papillary growth pattern, which raises the possibility of a high-grade papillary urothelial carcinoma. This lesion, however, has cells with true glandular differentiation with abundant eosinophilic cytoplasm and areas of tall columnar epithelium. This argues against a papillary urothelial carcinoma. Prostatic urethral polyps form polypoid urethral masses lined by completely benign prostatic secretory cells and are associated with benign appearing prostate glands.

Prostatic duct adenocarcinoma is an aggressive tumor that may present as a periurethral mass. There are two architectural patterns that may be seen, one of which is the papillary form seen in this case. The other shows cribriform nests of cancer. These tumors may also arise in more peripheral prostatic ducts and therefore can be sampled on prostate needle biopsies. Prostatic duct adenocarcinomas behave more aggressively than ordinary acinar adenocarcinomas, with more advanced pathologic stage at radical prostatectomy and having a higher recurrence rate.