Immunohistochemical demonstration of S100 protein in malignant melanoma and pigmented nevus, and its diagnostic application.

The presence of nervous tissue specific S100 protein was studied immunohistochemically in 47 cases of malignant melanoma and 25 pigmented nevi of various types of peroxidase-antiperoxidase immunoenzyme method on routine paraffin sections of the surgical specimens. Of 47 cases of malignant melanoma, 44 were positively stained for S100 protein. The intensity of S100 protein immunostaining was suggested to be inversely proportional to the amount of melanin pigment. In ten cases of 12 amelanotic melanomas, the immunoreaction for S100 protein in tumor cells was stronger than that of normal Bergmann glial cell in human cerebellum. Intradermal nevi and juvenile melanomas were strongly positive for S100 protein, but blue nevi contained little or no S100 protein. Our results suggest that S100 protein is widely distributed among melanotic tumors and is also a very useful diagnostic indicator for malignant melanoma, especially of the amelanotic type.