Answer: Squamous metaplasia

Histology: The seminal vesicle tissue in one area shows replacement by squamous cells that are associated with marked acute inflammation. Numerous mitotic figures can be seen in the squamous areas, however no atypical ones are identified.

Discussion: Squamous metaplasia in the seminal vesicles is not well-described in the literature. However, in this case, one can see that the squamous cells are cytologically bland and associated with an intense acute inflammatory infiltrate. The rounded nests seen within the stroma should not be misinterpreted as invasive squamous carcinoma. Rather, they represent squamous metaplasia in the seminal vesicle glands. There is one case in the literature describing invasive squamous carcinoma arising in the seminal vesicle, and it was postulated that the squamous carcinoma arose in the setting of inflammatory changes caused by obstruction of the ejaculatory duct. In contrast to the case shown here, however, the reported case showed overt malignant features.

Primary seminal vesicle carcinoma is exceedingly rare and is essentially a diagnosis of exclusion- other primary sites must be ruled out and the tumor must be localized to the seminal vesicle. Of the rare cases of primary seminal vesicle tumors, most are of the glandular type or adenocarcinomas. Urothelial carcinomas may rarely involve the seminal vesicles, either in the form of spread along the mucosa, or by direct stromal invasion. When a urothelial carcinoma spreads along the mucosa of the seminal vesicle, it may resemble squamous metaplasia, however urothelial carcinoma would show cytologic atypia that one can recognize as cancer, and the tumor is usually seen undermining the normal seminal vesicle epithelium.