Nodular Melanoma Mimicking Keratoacanthoma: Lessons to learn.

A 67-year-old man of Chinese descent presented with a painless nodular lesion that had been present on his right forearm for the previous 3 months. A single, well-defined, dome-shaped, firm nodule with a central keratin plug surrounded by erythema was noted. Keratoacanthoma with secondary bacterial infection was suspected and the patient underwent an excision biopsy. Biopsy of the nodule and immunohistochemical staining supported a diagnosis of nodular malignant melanoma. It should be noted both that nodular malignant melanoma may present with a wide variety of clinical appearances, and that the lack of melanin pigment in nodular malignant melanoma may hinder the diagnosis of this aggressive tumour.