A 67-year-old African American female presented with an approximately 18-month history of a solitary, asymptomatic lesion on the right leg. The patient's medical history was benign, and a review of systems only disclosed symptoms consistent with untreated menopause. The patient specifically denied trauma and local heat applications to the affected area. General physical examination was unremarkable with the singular exception of the irregularly shaped, darkly pigmented, slightly rough and scaly, 10 cm × 6.5 cm patch on the right foreleg. There was a 1.2 cm × 1.3 cm nodular component located in the superior pole of the lesion. Incidental note was made of innumerable small, hypopigmented macules scattered randomly from the ankles to the thighs bilaterally. There was no palpable inguinal adenopathy, and a recent routine laboratory panel disclosed very mild anemia and mild fasting hyperglycemia. A chest x-ray was normal.
This patient most likely has what tumor on her leg?