A 34-Year-Old Man Presents With an Expanding Lesion on the Right Arm

A 34-year-old, ostensibly healthy Caucasian male presented with a 3 cm × 3 cm solitary skin lesion located on the distal portion of the dorsal aspect of the right arm. The lesion first appeared during the patient’s last year in high school, approximately 17 years earlier. Although the lesion had always been asymptomatic, the patient was now concerned because of a recent expansion in size. The patient had extensive ultraviolet light exposure as a teenager while working as a lifeguard; excessive ultraviolet exposure continued as an adult due to outdoor employment as a geologic surveyor. The patient denied the use of sunscreen.  Family history was negative for similar lesions. The patient was not taking any medication.