A 75-year-old Caucasian woman was seen at a nearby community clinic for a raised lesion on her right thigh. She had noticed that the pale tan to light gray color of the lesion was changing. Examination by the referring experienced dermatologist showed a rough and coarsely granular, oval lesion with a slightly irregular border measuring 1.7 x 0.9 cm. Clinically, this lesion was thought to resemble an irritated seborrheic keratosis and was biopsied because of its size, a slight variability in color, and a clinical history of color change. The biopsy requisition diagnosis read Irritated Seborrheic Keratosis. Histopathologic examination of a deep-shave biopsy showed the low-power silhouette of a seborrheic keratosis, including squamous papilloma-like features and delicate, laminated pseudocysts of horn. The final diagnosis was malignant melanoma, superficial spreading type, Clarks level III, Breslow 1.44 mm, probable vertical growth phase, and simulating a seborrheic keratosis.Discussion QuestionOutline the diagnosis of skin cancer in this case, and compare and contrast the nature of basal cell carcinoma, squamous cell carcinoma, and malignant melanoma.