Anal canal carcinoma with Pagetoid spread: report of a case.

A 70-year-old man with a history of colon polyps was found to have a semipedunculated polyp in the anal canal. The patient was asymptomatic. The lesion was 14 mm in diameter and located 5 mm from the dentate line. Histological examination of biopsy specimens revealed well-differentiated adenocarcinoma of the anal canal. During transanal local excision of the tumor, an abnormality of the perianal skin was recognized. Although intraoperative frozen section of the perianal skin did not show malignancy, permanent sections of the perineal skin revealed Paget's cells in the epidermis. Pathological examination of the anal canal carcinoma revealed submucosally invasive well-differentiated adenocarcinoma with a positive distal surgical margin. Thus, we performed additional wide local excision of the perianal skin including the distal margin of the previous local excision. Pathological examination revealed continuance within the epidermis between the anal canal adenocarcinoma and Paget's cells in the perianal skin lesion. Scattered Paget's cells also formed some glandular structures. Thus, we concluded that the perianal skin lesion was Pagetoid spread of anal canal adenocarcinoma. This report shows that the perianal skin should be examined carefully in patients with anal canal carcinoma.