Distinguishing atrophy and high-grade prostatic intraepithelial neoplasia from prostatic adenocarcinoma with and without previous adjuvant hormone therapy with the aid of cytokeratin 5/6.

We evaluated the sensitivity and specificity of cytokeratin (CK) 5/6 for distinguishing foci of atrophy from prostatic adenocarcinoma with and without previous hormonal adjuvant therapy and observed the intensity and pattern of staining in mimickers of prostatic adenocarcinoma (basal cell hyperplasia, atypical adenomatous hyperplasia, and tangentially cut high-grade prostatic intraepithelial neoplasia [PIN]). We reviewed 146 acinar proliferations in 81 specimens (radical prostatectomy, previously untreated, 41; radical prostatectomy, following androgen-deprivation therapy, 11; transurethral resection, previously untreated, 29). All benign acinar proliferations stained positively for CK5/6, with immunoreactivity restricted to basal cells. Untreated and androgen-deprived prostatic adenocarcinomas were invariably negative. The pattern of staining was continuous in 79% of the atrophy cases (15/19), and all foci stained with CK5/6. Characteristic double-layer staining in basal cell hyperplasia was observed in 93% of cases (13/14), and foci of high-grade PIN had a characteristic "checkerboard" staining with areas of discontinuity. Foci of atypical adenomatous hyperplasia showed continuous staining, including cauterized acini in 53% of cases (8/15), with a fragmented basal cell layer pattern in 47% of cases (7/15). CK5/6 staining of the basal cells in foci of atrophy is sensitive and specific for excluding prostatic adenocarcinoma with and without androgen-deprivation effect.