The value of S-100 immunostaining as a diagnostic tool in human malignant melanomas. A comparative study using S-100 and neuron-specific enolase antibodies.

The brain proteins S-100 and neuron-specific enolase have been reported by separate groups to be present in human malignant melanomas. There is no systematic study comparing the occurrence of these proteins in the same tumour specimens. We have examined 33 primary malignant melanomas, including 5 which were amelanotic, and 25 metastatic melanomas using immunohistochemical methods with specific, non-cross-reacting antibodies to S-100 and NSE. We found S-100 immunoreactivity to be present in all cases but one, whereas NSE immunoreaction was very weak and patchy, and present in only 6 cases. S-100 immunoreactivity was not demonstrated in 40 control tumours, either primary or metastatic in skin, including basal- and squamous-cell carcinomas, spindle-cell sarcomas, lymphomas and Merkel cell tumours. All intradermal (n = 4) and compound (n = 1) naevi were positive for S-100, 2 blue naevi showing much less reaction. NSE immunoreactivity was detected in Merkel cell tumours (n = 8), undifferentiated (n = 2) and small cell (n = 1) carcinomas, and all melanocytic naevi. It is suggested therefore that antibody to S-100 is the reagent of choice for demonstration of melanocytic tumours, and may be especially valuable in the diagnosis of amelanotic melanoma or metastatic tumours of doubtful origin where melanoma is suspected.