Serum protein s100beta in patients with malignant melanoma detected by an immunoluminometric assay.

S100 protein is well established as a diagnostic tool in malignant melanoma immunohistology. In this study we measured S100beta in serum with a recently developed luminometric immunoassay with a detection limit of 0.02 microg/l. By measuring S-100beta in a group of apparently healthy individuals a mean value of 0.031 +/- 0.026 microg/l was found. In the reference group, serum S100beta was below 0.12 microg/l in all cases. To assess the sensitivity of the assay we investigated serum S-100beta levels in 371 serum samples of 315 patients with histological proven malignant melanoma at different disease stages. Staging was performed according to the German Society of Dermatology classification. Significant differences were observed between the control 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). S100beta > 0.20 microg/l helps to distinguish between tumour-free and tumour-bearing patients with a specificity of 97.0% and a sensitivity of 64.6%. Our results demonstrate the serum S100beta is of limited value as a melanoma marker. However, it has clinical significance for identifying tumour-positive patients in advanced malignant melanoma stages III and IV.