Malignant melanoma with a rhabdoid phenotype exhibiting numerous solid tumor masses: a case report.

We present a case of malignant melanoma with a rhabdoid phenotype in a 44-year-old female with a quite unique and aggressive clinical course. Rhabdoid features are defined by characteristics such as sheets or solid trabeculae of neoplastic cells with large, vesicular, round to bean-shaped nuclei, prominent centrally located nucleoli, and abundant eccentric cytoplasm. Although various histological differential diagnoses were cited for the present case that showed 'rhabdoid features', most of them were excluded on the basis of the clinical history, tumor location, clinical behavior, and a broad panel of immunohistochemical stains. In the present case, the immunohistochemical findings were positive for vimentin, S-100 protein, melan-A, and EMA, but negative for HMB45, cytokeratin, CD34 and desmin. In addition, the positive expression of BAF47 was also recognized. These findings lead to the conclusion that this quite unique aggressive soft tissue tumor should therefore be diagnosed as malignant melanoma with a rhabdoid phenotype.