Perianal Paget disease associated with non-invasive colorectal adenoma

Perianal skin Paget disease (PPD) is an unusual subtype of extramammary Paget disease, which is usually caused by a primary intraepithelial adnexal tumor and secondary spread from colorectal adenocarcinoma. The reports of secondary PPD associated with non-invasive colorectal adenoma are rare. We report a rare case of non-invasive colorectal-adenoma-associated PPD. In this case, the intraepithelial Paget cells of perianal skin manifested with colorectal phenotype by immunohistochemistry, and adjacent adenomas had high-grade intraepithelial neoplasia but not invasion. Although this is a rare manifestation of PPD, understanding this phenomenon is important to prevent overdiagnosis and invasive overtreatment. Clinical management is variable and, therefore, close follow-up examination is necessary.