Distinctive immunohistochemical profile of penile intraepithelial lesions: a study of 74 cases

Several classification schemes for penile precancerous lesions have been proposed, but none of them seems to correlate with the current understanding of penile cancer pathogenesis. Recently, a system, which takes into account morphologic features and purported etiopathogenesis, was proposed, separating penile intraepithelial neoplasia (PeIN) in differentiated and warty/basaloid subtypes. This study was designed to seek an immunohistochemical profile that can be helpful in the classification and differential diagnosis of penile epithelial abnormalities and precancerous lesions using the aforementioned system. The immunohistochemical panel included stains for p16, p53, and Ki-67. For p16 immunostaining, only full-thickness positivity in all epithelial cells was considered as positive; for p53 and Ki-67 immunostaining, patchy or diffuse nuclear positivity above the basal layer was considered as positive. Seventy-four lesions in 59 patients were selected and classified as follows: differentiated PeIN, 34 cases; squamous hyperplasia (SH), 21 cases; basaloid PeIN, 15 cases; and warty PeIN, 4 cases. The mean age of patients was 64 years. Forty-two lesions (56.8%) were located in the glans and 32 (43.2%) in the foreskin. Overexpression of p16 was useful for distinguishing SH from warty/basaloid PeINs (0% vs. 94.7%, P<0.0001) but not SH from differentiated PeINs (0% vs. 5.9%, P=0.519). In addition, p16 allowed the distinction of differentiated and warty/basaloid PeINs (5.9% vs. 94.7%, P<0.0001). Immunohistochemistry results for p53 allowed the separation of SH and differentiated PeIN (9.5% vs. 44.1%, P=0.0078) and SH and warty/basaloid PeIN (9.5% vs. 55.6%, P=0.0042). Ki-67 immunostain was useful for distinguishing SH from differentiated PeIN (52.6% vs. 89.7%, P=0.0062) and SH from PeIN with warty and/or basaloid features (52.6% vs. 100%, P=0.0011). There seems to be a distinctive immunohistochemical profile for associated and precursor epithelial lesions of the penis. SH was p16 and p53 negative, with variable Ki-67 positivity. Differentiated PeIN was p16 negative and Ki-67 positive, with variable p53 positivity. Basaloid and warty PeINs were consistently p16 and Ki-67 positive, with variable p53 positivity. The use of a triple p16/p53/Ki-67 immunohistochemical panel was found to be helpful in the classification, differential diagnosis, and morphologic standardization of penile intraepithelial lesions.