Sclerosing adenosis of the prostate. Histopathologic and immunohistochemical analysis.

A prostatic lesion, histologically identical to sclerosing adenosis of the breast, was found in five (1.9%) of 263 patients who underwent transurethral resection, open prostatic adenectomy, radical prostatectomy, or total cystoprostatectomy. This uncommon lesion was a localized proliferation of crowded small glands, small solid nests, and individual cells embedded in a cellular stroma, mimicking a small acinar prostatic adenocarcinoma. The proliferating glands were lined by a single layer of secretory cells surrounded by an eosinophilic membranous structure. Basal cells were disclosed in individual glands or as small nests and even individual cells with immunostainability for basal cell-specific cytokeratin (EAB903), S-100 protein, and muscle-specific actin (HHF35). These findings indicate the benign nature of the lesion with myoepithelial differentiation of the basal cells. In contrast, all 25 small acinar adenocarcinomas examined as controls lacked positive stains for the above three antibodies, verifying the usefulness of these antibodies to distinguish between this benign lesion from adenocarcinoma.