Papillated squamous cell carcinoma in situ arising in a seborrheic keratosis

A 73-year-old man had developed a 27 x 60-mm seborrheic keratosis on his trunk. Some months previously, an 18 x 19-mm cauliflower-like area had developed within this seborrheic keratosis. Histologic examination showed a papillated squamous cell carcinoma in situ arising in a seborrheic keratosis. Seborrheic keratoses are the most common cutaneous neoplasms in man. Malignant changes are most unusual but should be suspected in lesions of unusual clinical appearance.