Primary cutaneous melanoma of the buttock: does injury from ultraviolet light play a role?

A 38-year-old man, initially referred for Mohs' surgery of a facial skin cancer, was found to have a thin (less than 0.5 mm thick, Clark Level II) primary cutaneous melanoma of the buttock. The melanoma, previously unnoticed by the patient, was 0.5 cm in diameter. Sunburn, a widely recognized risk factor for primary cutaneous melanoma, had occurred on the patient's buttocks during skinny dipping 20 years earlier. Traumatic injury due to ultraviolet light exposure may explain the subsequent development of some skin cancer on sites ordinarily protected by clothing.