Examination of hematoxylin-eosin–stained sections of the biopsy specimens showed a predominantly neutrophilic vascular and perivascular infiltrate with areas of fibrinoid necrosis. Capillaries and lymphatic vessels were dilated, and focal fibrinoid changes were observed in blood vessel walls. Other sections had a mixed neutrophilic and lymphocytic infiltrate with red blood cell extravasation and dermal edema. Special stains (gram, Fite, and methenamine silver) were all negative for microorganisms. Considered together, these findings were most consistent with leukocytoclastic vasculitis, with features of urticarial vasculitis. The vasculitis was thought most likely to be due to the patient’s underlying carcinosarcoma. The patient was given 12 mg of methylprednisone intravenously in a single dose. By the following morning, the swelling, erythema, and pain in his hands had decreased markedly. A slow taper of oral prednisone was prescribed, starting at a dosage of 60 mg/d. The patient’s skin eruption had improved more than 50% by the time of hospital discharge 4 days later. At the 3-week follow-up evaluation, the symptoms had entirely resolved, and the tapering of the prednisone therapy was completed over the next 3 weeks, without a return of symptoms.