Malignant melanomas contain only the vimentin type of intermediate filaments.

Six malignant melanomas have been examined for the type of intermediate filament they contain. All six cases showed positive staining of intermediate filaments with antibodies to vimentin, with cells containing large numbers of melanosomes being stained less strongly in general. The tumor cells did not react with antibodies to keratin, desmin, neurofilaments or glial fibrillary acidic protein. Thus typing of intermediate filaments can distinguish melanoma from undifferentiated carcinoma, but not from lymphoma or sarcoma. Since melanocytes are known to be vimentin positive, and since most of the samples we studied were from metastases, these results are a further indication that the intermediate filament type typical of the parental cell is retained in the metastases, as well as in the primaries of solid tumours. The implications of vimentin positivity for the histiogenesis of the melanocyte are also discussed.