Postatrophic hyperplasia of the prostate. A histologic mimic of prostatic adenocarcinoma.

Clusters of atrophic prostatic acini that display proliferative epithelial changes are referred to as postatrophic hyperplasia (PAH). PAH is histologically similar to adenocarcinoma and may cause diagnostic confusion. Despite the importance of distinguishing PAH from carcinoma, the last systematic study of this lesion was reported > 40 years ago, and many contemporary pathologists are unfamiliar with this lesion. We reviewed 100 consecutive whole-mount radical prostatectomy specimens removed for carcinoma to determine the incidence of PAH. In addition, 11 prostatic needle biopsy specimens with PAH were evaluated to further characterize the lesion in limited specimens. PAH was identified in 18 radical prostatectomies (18%), including 10 unicentric and eight multicentric cases. It was found exclusively in the peripheral zone in all but two cases, which had additional involvement of the transition zone. PAH consisted of a microscopic lobular cluster of small acini with irregular atrophic-appearing contours lined by cuboidal cells with mild nucleomegaly and micronucleoli; mildly enlarged nucleoli were focally present in 39% of cases. Within the small acinar cluster, a larger dilated acinus was usually present centrally, which was lined by flattened to cuboidal epithelial cells. The basal cell layer at the periphery of each acinus was invariably present but often inconspicuous. Immunohistochemical staining for high-molecular-weight keratin (antibody 34 beta E12) showed the presence of an intact basal cell layer in seven of 10 cases and a focally fragmented basal cell layer in three other cases. PAH was associated with patchy chronic inflammation in 16 of 18 prostatectomy cases; stromal changes were present in all cases, ranging from smooth atrophy to dense sclerosis with compression of acini. No intraluminal basophilic mucin was identified, but two needle biopsies showed PAH with focal mucinous metaplasia. Crystalloids were not seen in any case. Focal partial acinar involvement by high-grade prostatic intraepithelial neoplasia was present in adjacent acini in two cases. Adjacent acini also invariably showed typical changes of atrophy. In the needle biopsy specimens, PAH showed the same features as those in prostatectomies, but often only a portion of the lesion was sampled. PAH is distinguished from carcinoma by its characteristic architecture, intact or fragmented basal cell layer, inconspicuous or mildly enlarged nucleoli, and adjacent acinar atrophy with stromal fibrosis or smooth muscle atrophy. Distinguishing PAH from carcinoma is most difficult in needle biopsy specimens in which only a portion of the lesion is sampled, and awareness of this entity assists in this distinction.