Four months ago, this 23-year-old man developed a lesion on his right shoulder. It appeared, as he recalls, over the course of a week and has subsequently grown. The lesion, which is now rather large, bleeds copiously with minor trauma. It causes only modest discomfort to the patient but considerable worry to his family.
The lesion was originally tiny and tag-like; the patient initially mistook it for a tick and tried to pull it off. Not only did that fail to work, it also seemed to irritate the lesion. At that point, it started to swell, eventually transforming into the lesion he presents with today.
The patient’s history is otherwise uneventful, and he reports taking no medications. He has had minimal sun exposure but says he tans easily when he does get some sun.
The lesion, measuring 5 mm x 2.5 mm, is a dark red and pedunculated papule on the crown of the right shoulder. It looks edematous and feels firm. The patient has otherwise unremarkable type IV skin.
Shave biopsy is performed, using a double-edged razor to make a shallow concave defect under the lesion. The wound is cauterized.
What is the diagnosis?