Birthmark on the chest

A 15-year-old adolescent with a birthmark on her chest presents to the dermatology clinic for evaluation. The lesion was first noticed at birth and has grown as the patient has aged, becoming increasingly thick and dark over the years. The patient reports that the lesion is not painful, itchy, or bleeding, but she is somewhat bothered by its appearance. On physical examination, there is a well-demarcated, oval, dark brown plaque with a pebbly texture on the patient's right upper chest.