This patient had a past history melanoma (three years earlier) making this the likely diagnosis. He went on to have surgery.
MICROSCOPIC DESCRIPTION: Paraffin sections show a densely hypercellular tumor. Tumor cells have markedly pleomorphic round and oval vesicular nuclei with conspicuous nucleoli and a variable amount of pale cytoplasm. These are arranged in diffuse sheets within a vascular stroma. Frequent mitotic and apoptotic figures are identified and there is extensive tumor necrosis. Tumor cells show strong immunostaining for tyrosinase and Sox 10. No staining for TTF-1, carcinoembryonic antigen (CEA), pancytokeratin AE1/AE3 or for cytokeratins CK7 and CK5&6 is seen in tumor cells. The features are of metastatic malignant melanoma.