S100B protein, 5-S-cysteinyldopa and 6-hydroxy-5-methoxyindole-2-carboxylic acid as biochemical markers for survival prognosis in patients with malignant melanoma

Elevated levels of the phaeomelanin metabolite 5-S-cysteinyldopa and the eumelanin metabolite 6-hydroxy-5-methoxyindole-2-carboxylic acid in urine and serum have been shown in previous studies to correlate with disseminated malignant melanoma. Immunohistochemical detection of S100B protein is an acknowledged method for the diagnosis of malignant melanoma, and it has been suggested that rising serum levels of S100B protein are associated with the survival rate of patients with malignant melanoma. In the present study serum levels of S100B protein and urinary concentrations of 5-S-cysteinyldopa and 6-hydroxy-5-methoxyindole-2-carboxylic acid were measured in 91 patients with histopathologically verified malignant melanoma. At the time of sampling 13 patients were in clinical stage I, 13 in stage II and 65 in stage III. The urinary levels of the melanin metabolites were determined by automated high performance liquid chromatography, and the serum levels of S100B protein by an immunoradiometric assay with two monoclonal antibodies. The overall survival rate was most strongly associated with the serum levels of S100B protein (P < 0.001), but there was also a significant correlation to urinary levels of 5-S-cysteinyldopa (P < 0.001). A corresponding association with urinary levels of 6-hydroxy-5-methoxyindole-2-carboxylic acid was found in only a very few patients with extremely high urinary concentrations. A statistically significant increase in relative hazard was found for S100B protein levels exceeding 0.6 mu g/l (P < 0.001), and predictably for patients in clinical stage III (P < 0.001). An analysis of S100B protein levels in patients in clinical stage III showed a significant correlation to survival (P = 0.005). Our study suggests that of the three biochemical tumour markers, S100B and to a lesser extent 5-S-cysteinyldopa have the greatest potential to be used as predictors of survival prognosis in patients with malignant melanoma.