Role of preoperative topical 5-fluorouracil in preparation for Mohs micrographic surgery of extramammary Paget's disease.

The true extent of the skin affected in extramammary Paget's disease is frequently well beyond its clinical borders. A case of extramammary Paget's disease of the scrotum was treated with Mohs micrographic surgery. Prior to surgery, 5-fluorouracil was applied topically for 10 days. This resulted in a sharply delineated, erythematous patch of biopsy-proved extramammary Paget's disease well beyond the original clinical borders. This increased the visible area of disease by 60%. Mohs micrographic surgery detected microscopic extramammary Paget's disease approximately 1 cm beyond the erythematous borders. The location of disease farthest from the margins was in the direction toward which this erythema was most advanced when the application of 5-fluorouracil was discontinued. At the time of writing, 3.5 years after treatment, the patient was free of disease. Topical 5-fluorouracil may have a role as an adjunct to surgery by highlighting subclinical areas of extramammary Paget's disease. It may also be useful postoperatively to detect early disease recurrence.