Basal cell carcinoma of the prostate: unusual subtype of prostatic carcinoma.

Basal cell carcinoma of the prostate, which has been generally considered to be indolent, is an unusual histological type of prostatic carcinoma and is extremely rare. This tumor has been classified according to the prevalent pattern of growth as adenoid cystic carcinoma or basaloid cell carcinoma (BCC), with the former growth pattern being considered to be the main feature of this entity. A 67-year-old Japanese man was admitted to a general hospital with obstructive urinary symptoms. His prostate was slightly enlarged, stony hard, and with a rough surface on digital rectal examination, while serum prostate-specific antigen and prostatic acid phosphatase concentrations were within the normal ranges (0.007 and 0.9 ng/mL, respectively). 2-Fluoro-2-deoxy-D-glucose-positron emission tomography/computed tomography (FDG-PET/CT) exhibited multiple accumulations suspicious for cancer metastases. Specimens obtained by prostatic needle biopsy showed immunohistochemical reactivity for cytokeratin 34βE12 and P63, findings that were identical to those seen in basal cell carcinoma. Basal cell carcinoma of the prostate is a rare tumor, reported in 56 cases so far, and among all these, the pure form of BCC is extremely rare. Immunohistochemistry is indispensable to distinguish this neoplasm from other unusual histological types of prostatic carcinomas. Our findings reveal that tumors with a basaloid cell-predominant pattern have significant potential for a poor prognosis, in contrast with the conventional understanding regarding this neoplasm.