Answer: Paraganglia

Histology: Two different cases with the same lesion are illustrated. In the first few images, a collection of cells is seen outside the prostate. At higher magnification, this focus consists of nests of cells with bland nuclei and granular amphophilic cytoplasm. A thin vascular network separates the nests. In the second set of images, a similar nest is seen although the grouping of cells into nests and the vascularity is not as obvious.

Discussion: High-grade adenocarcinomas of the prostate, while consisting of solid nests or sheets of cells, would not be expected to be present as a tiny focus on needle biopsy. Furthermore, it would be exceedingly rare to have as the only focus of cancer on biopsy, high-grade cancer present outside of the prostate on needle biopsy. The bland cytology further argues against adenocarcinoma of the prostate. In the first case, the striking amphophilic cytoplasm, as well as the nested appearance of the cells separated by the vascularity, is typical of paraganglia cells. Paraganglia cells have the identical morphology to paraganglioma except for it being an incidental microscopic focus. Carcinoid tumors of the prostate are exceedingly rare, and would be composed of a large mass of cells, possibly similar in morphology to paraganglia. If there is a question as to whether a focus represents paraganglia or adenocarcinoma of the prostate, neuroendocrine stains can be performed, which would be positive. Stains for S-100 will show a sustentacular pattern. Stains for prostatic markers would be negative.