Serum protein S100 beta in patients with malignant melanoma detected by animmunoluminometric assay

S100 protein is well established as a diagnostic tool in malignant melanoma immunohistology. In this study we measured S100 beta in serum with a recen tly developed luminometric immunoassay with a detection limit of 0.02 mu g/ l. By measuring S-100 beta in a group of apparently healthy individuals a m ean value of 0.031 +/- 0.026 mu g/l was found. In the reference group, seru m S100 beta was below 0.12 mu g/l in all cases. To assess the sensitivity o f the assay we investigated serum S-100 beta levels in 371 serum samples of 315 patients with histological proven malignant melanoma at different dise ase stages. Staging was performed according to the German Society of Dermat ology classification. Significant differences were observed between the con trol group and stages IIb (P = 0.01) and IV (P = 0.001). In tumour-bearing patients of stages IIIb and IV, the difference was highly significant (P < 0.0001). S100 beta > 0.20 mu g/l helps to distinguish between tumour-free a nd tumour-bearing patients with a specificity of 97.0% and a sensitivity of 64.6%. Our results demonstrate the serum S100 beta is of limited value as a melanoma marker. However, it has clinical significance for identifying tu mour-positive patients in advanced malignant melanoma stages III and IV.