OBJECTIVETo investigate the clinicopathological features and the immunohistochemical phenotype of perianal Paget's disease (PPD) associated with internal anorectal adenocarcinoma, with emphasis on the histogenesis of Paget's cells.

METHODSThe clinical and pathologic features of three cases of PPD with rectal adenocarcinoma were investigated. Periodic-acid-Schiff (PAS), alcian-blue and mucicarmine staining with and without diastase digestion were performed. The immunohistochemical study was performed on selected sections by a panel of antibodies including carcinoembryonic antigen (CEA), CK7, CK8, CK10/13, CK20 and gross cystic disease fluid protein 15 (GCDFP15).

RESULTSAll three cases occurred in middle to old age male patients complaining of anal bleeding. Digital physical examination revealed ulcerated or cauliflower-like masses in the anus just distal to the dentate line. Perianal skin erythematous patches were found in two cases, and small discrete granules in one case. Histologically, the anorectal neoplasm was either a moderately or poorly differentiated adenocarcinoma. Two types of Paget's cells were noted, namely the classical type characterized by a polygonal shape with vesicular nuclei and abundant pale cytoplasm, and the signet ring type characterized by eccentrically displaced nucleus. Both the rectal adenocarcinoma cells and Paget's cells showed strong positivity for PAS, AB and mucicarmine, which were resistant to the diastase digestion. Immunohistochemically, they were both positive for CEA, CK7, CK8 and CK20, but negative for CK10/13 and GCDFP15.

CONCLUSIONSThe CK20(+)-GCDFP15(-) type Paget's cells in PPD were derived from the direct intraepithelial Pagetoid spread of anorectal adenocarcinomas. PPD was more frequently associated with internal carcinomas than any other type of extramammary Paget's disease. It is recommended that clinicians should carefully examine the anus or rectum in the presence of PPD to ascertain if it is associated with an internal carcinoma.