Pagetoid Squamous Intraepithelial Neoplasia of the Vulva as a Mimicker of Vulvar Extramammary Paget Disease: Two Cases with Basal Layer Sparing.

Human papillomavirus-associated vulvar intraepithelial neoplasia (high-grade squamous intraepithelial neoplasia [HSIL] or VIN of usual type) is a lesion characterized by atypia extending from the basal layer to the upper epidermis. There are only rare reports of vulvar intraepithelial morphology exhibiting a pagetoid pattern of intraepithelial dissemination. We herein report two cases of vulvar HSIL in which a pagetoid pattern of spread and a largely uninvolved basal layer represented a diagnostic pitfall for extramammary Paget disease. Nuclear atypia reminiscent of HSIL in addition to expression of p16, KRT5/6, and p40 were however in favor of pagetoid HSIL. Although there is morphological and immunohistochemical overlap between these two entities, an accurate diagnosis is important, since an erroneous diagnosis of vulvar extramammary Paget disease may lead to an extensive workup comprising radiological imaging, colonoscopy, and cystoscopy.