Answer: Basaloid carcinoma

Histology: This tumor shows multiple different patterns. One pattern consists of large basaloid nests with central comdeonecrosis. The cells lining these nests show scant cytoplasm, small nucleoli, with relatively rare mitotic figures. The cells appear fairly uniform one to another. Focally within some of these basaloid nests there is evidence of luminal differentiation. The tumor shows another pattern analogous to what is seen in salivary glands with nests and cells surrounded by a hyaline basement membrane-like substance. Focally, the tumor shows squamous differentiation. Finally, a pattern of the tumor consists of small tubules lined by multiple rows of basaloid cells with fairly bland cytology.

Discussion: Small cell carcinoma of the prostate could show similar basaloid nests with necrosis. However, small cell carcinoma of the prostate as in other organs is typified by a brisk mitotic rate with numerous apoptotic bodies, which are lacking in the current case. Furthermore, the cells lack the nuclear molding classically seen with small cell carcinoma. One of the patterns of Gleason pattern 5 adenocarcinoma of the prostate is that of nests of tumor with comdeonecrosis. However, adenocarcinoma of the prostate shows more abundant cytoplasm with typically large prominent nucleoli as opposed to what is seen in the current case. In contrast to Gleason pattern 3, the individual glands seen in the current case show multilayering of their cells with atrophic cytoplasm. Many of the smaller glandular structures seen in the current case with multi-laying of the nuclei by themselves are typical of basal cell hyperplasia. However, the presence of these larger nests with necrosis is beyond what one could see with basal cell hyperplasia. Furthermore, some of these smaller nests resembling basal cell hyperplasia appear to be infiltrating thicker muscle bundles suggestive of bladder neck muscle. Consequently, the best diagnosis in this case is that of a basaloid carcinoma. Basaloid carcinoma of the prostate may show a range of histology as seen in the current case. Some of the patterns resemble basal cell hyperplasia and are only diagnosed as malignant based on their extension into extra-prostatic tissue which would be inconsistent with basal cell hyperplasia. One of the patterns of basaloid carcinoma seen in the current case resembles that of adenoid cystic carcinoma of the salivary gland. Consequently, some of these tumors in the past have been called adenoid cystic carcinoma of the prostate. I prefer to consider all of these tumors under the more descriptive category of basaloid carcinoma of the prostrate. Up until recent times, these tumors were not known to have the ability to metastasize to different sites. A more recent study, that is not yet published, documented that in some of these cases distant metastases may occur in addition to advanced local growth. One cannot distinguish basal cell hyperplasia from basaloid carcinoma based on high molecular cytokeratin stains as both are positive. However, we have demonstrated that basaloid carcinomas may over express BCL-2 and KI67 relative to that of basal cell hyperplasia (Hum Pathol 1998; 29: 1447-1450).