Sclerosing adenosis of the prostate. Report of three cases with electronmicroscopy and immunohistochemical study

Three cases of a rare variant of prostatic adenosis with the features of sclerosing adenosis, an uncommon lesion sometimes confused with prostatic carcinoma, are reported. The lesions consisted of a small, single nodule in prostates otherwise showing typical adenomatous and fibromuscular hyperplasia. The lesions were composed of crowded small glands, small solid nests and individual cells embedded in a cellular stroma. Immunohistochemistry showed that the glands were lined by basal cells positive for high‐weight keratins (EAB‐903 and AE‐3), a finding which confirms the benign nature of the lesion. S‐100 protein and smooth muscle actin were also positive in the same basal cells suggesting myoepithelial differentiation, a character not found in basal cells outside this lesion. This finding was confirmed at ultrastructural level by the finding of numerous thin filaments in the cytoplasm of basal cells. It is important to recognize this lesion in order to avoid confusion with well‐differentiated prostatic carcinoma.