Perianal Paget's Disease Co-Associated with Anorectal Adenocarcinoma: Primary or Secondary Disease?

Perianal Paget's disease (PPD) represents a skin neoplasm which can be either primary or secondary to carcinoma from an adjacent internal organ. PPD with underlying colorectal adenocarcinoma is usually looked upon as a secondary disease. We report a rare case of co-associated PPD and anorectal adenocarcinoma. The PPD was found to be located near the anorectal adenocarcinoma with normal tissues between them. Immunohistochemical stains demonstrated that the Paget's cells were CK7+/GCDFP-15-/CK20-/MUC2-/CDX2-, whereas the anorectal adenocarcinoma was shown to be CK7+/GCDFP-15-/CK20+/MUC2+/CDX2+. This immunological phenotypic profile supported the notion that PPD and anorectal adenocarcinoma were of different origins, but could not define the exact origins of PPD. In our determination, this case was a primary PPD with anorectal adenocarcinoma. PPD remains a heterogeneous and complex pathology, and additional studies are required to differentiate between the various possible origins.