Unifocality of extramammary Paget disease.

Extramammary Paget disease is a rare tumor that often is associated with multiple recurrences after wide local excision. Over the years, the theory that this tumor is multicentric has been accepted without detailed scrutiny. We describe a patient with unifocal extramammary Paget disease. Axillary extramammary Paget disease was treated with Mohs micrographic surgery and intraoperative cytokeratin 7 immunostaining. With the use of the information from scouting biopsies and the Mohs map, a two-dimensional recreation of the tumor showed two contiguous, thin, long, finger-like projections extending from the main body of the tumor. Extramammary Paget disease may be a contiguous tumor with a highly irregular pattern of spread on the skin. It can have finger-like projections beyond the main body of the tumor. These subclinical projections may not be observed with routine hematoxylin-eosin staining. Cytokeratin 7 immunostaining is required to visualize Paget cells that extend beyond the main body of the tumor.