Malignant melanoma with pseudocarcinomatous hyperplasia--an entity that can simulate squamous cell carcinoma. A light-microscopic and immunohistochemical study of four cases.

We report four unusual cases of malignant melanoma in which squamous cell carcinoma was strongly considered in the differential diagnosis on routine hematoxylin and eosin-stained sections due to the near absence of melanin and the presence of pseudocarcinomatous hyperplasia. Ultimately, immunohistochemical staining for S-100 protein and keratin established the correct diagnosis of malignant melanoma in all cases.