S100 protein: a marker for human malignant melanomas?

S100 protein is a nervous-system-specific cytoplasmic protein which is also present in human malignant melanoma cell lines. To test for its tumour specificity, biopsy specimens from normal tissue and a wide variety of tumours were tested for S100 by complement fixation and immunofluorescence tests. S100 was present in all of thirteen samples of malignant melanoma tissue and absent from nineteen samples of non-melanocytic tumours, and from normal skin and normal lymph nodes. S100 levels did not correlate with tyrosinase activity in the tissues examined. Detection and measurement of S100 protein may help distinguish poorly differentiated amelanotic malignant melanoma from tumours of obscure histological origin; they may also aid the detection of micrometastatic disease in the lymph nodes and other tissues of melanoma patients.