Detection of S-100 protein in melanocytic and neurogenic cutaneous tumors

Quantitative determination of S-100 protein content on human melanoma tissues and in sera of melanoma patients was made possible through radioimmunoassay (RIA). Melanoma tissue extracts prepared from metastatic sites in both skin and lymph nodes contained 0.08-2.80% of S-100 out of the total extractable proteins, and it was also noticed that the tumors obtained from lymph-node metastasis possessed slightly higher levels of S-100 as compared with those obtained from the skin lesions. Serum S-100 levels of 12 melanoma patients with Stage 1 to 3 diseases were also examined by means of RIA, but only two patients showed a slight elevation of serum S-100 levels. When tissue sections prepared from a variety of cutaneous tumors, including pigmented nevus, melanoma and Schwannoma, were stained for S-100 by an immunoperoxidase technique, these tumors of neuroectodermal origin were demonstrated to contain a detectable amount of S-100, whereas other tested nonmelanocytic and non-neurogenic tumors were entirely negative for S-100. These data stress the usefulness of S-100 for the diagnosis of neurogenic and melanocytic tumors, especially melanomas, despite the difficulty of its detection in the sera of the tumor bearers, which might reflect the low tendency of S-100 to be shed from the tumor cells.