A case of an adverse reaction to topical 5-fluorouracil in irradiated skin.

A 73-year-old Caucasian male was treated in the dermatology clinic for squamous cell carcinoma (SCC) of the scalp by Mohs micrographic surgery. The patient subsequently received radiation therapy because of possible calvarium invasion. Approximately 2 years later, the patient developed Bowen's disease within the previously irradiated skin flap. The lesion was treated with topical 5-fluorouracil (5-FU) twice daily for 4 weeks, and subsequently developed a 2 x 2 cm full-thickness ulceration with exposed calvarium.