Malignant Melanoacanthoma.

Melanoacanthomas are benign variations of seborrheic keratosis that have been known to mimic other common benign and malignant skin lesions. Therefore, the diagnosis typically requires biopsy and careful histologic examination. Here, we present the case of a 25-year-old woman initially diagnosed clinically with an epidermal inclusion cyst, but, on biopsy and further evaluation, was found to have histological features of an atypical or malignant melanoacanthoma. Contrary to typical cases of melanoacanthoma, histologic evaluation revealed atypical findings consistent with malignancy, such as tumor necrosis, marked cytologic atypia and pleomorphism, and numerous mitoses, including atypical forms, features consistent with malignancy (ie, similar to a squamous cell carcinoma in these areas). This report highlights the importance of histological evaluation in diagnosis and treatment of skin lesions because atypical presentations often occur and can delay correct diagnosis and appropriate treatment.