Adenosis of the prostate. Histologic features in transurethral resection specimens.

Adenosis (atypical adenomatous hyperplasia, small gland hyperplasia) of the prostate is characterized by a relatively well-circumscribed proliferation of benign glands that frequently mimics low-grade adenocarcinoma. Although general reviews of adenosis exist, relatively few specialized studies have characterized the histologic features of adenosis. The purpose of this study was to review and better document the histologic features of adenosis. Forty-four transurethral resection (TUR) specimens containing a total of 145 foci of adenosis were evaluated for the presence or absence of six histologic features: mitotic figures, blue-tinged luminal mucinous secretions, intraluminal crystalloids, single cells, a focally infiltrative growth pattern, and prominent nucleoli. Immunohistochemical stains for high-molecular-weight cytokeratin were performed on 66 (46%) of the foci to confirm the presence of a basal cell layer and thus the diagnosis of adenosis. Crystalloids were present in 58 foci (40%), an infiltrative growth pattern in 27 foci (19%), single cells in 23 foci (16%), prominent nucleoli in 22 foci (15%), mitotic figures in 16 foci (11%), and blue-tinged luminal mucinous secretions in 3 foci (2%). The diagnosis of adenosis is based on a constellation of histologic features and may be confirmed with the use of antibodies to high-molecular-weight cytokeratin.