An 87-year-old female patient presented with hematochezia. Clinical examination revealed an elevated, erythematous lesion on the perianal skin. Imaging studies, including computed tomography, showed edema of the rectal mucosa with enlargement of the regional lymph nodes, particularly the left inguinal and aortic nodes. Colonoscopy revealed a 20 mm high lesion on the rectal mucosa, which was not in continuity with the perianal lesion. Histopathological analysis of both the perianal skin and the rectal biopsy confirmed the diagnosis of colorectal cancer, with subsequent identification of pagetoid spread from the rectal malignancy. Differentiating between perianal Paget's disease and pagetoid spread originating from nearby carcinomas is a diagnostic challenge, and the use of immunohistochemical staining is proving to be an invaluable adjunct. In the presence of perianal mucosal lesions, colonoscopy is strongly recommended to assess the potential for pagetoid spread from other primary sites.
