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.