Prognostic value of serum analyses of S-100 beta protein in malignant melanoma.

S-100 protein was first described in the central nervous system but is also present in malignant melanoma cells. Immunohistochemical detection of S-100 is widely used in the histopathological diagnosis of malignant melanoma. In the present study serum levels of S-100 beta protein were measured in 643 patients with cutaneous malignant melanoma. An immunoradiometric assay with three monoclonal antibodies against bovine S-100 protein beta subunit was used. At the time of blood sampling 553 patients were in clinical stage I, 24 in clinical stage II and 66 in clinical stage III. The overall survival rate was strongly associated with serum levels of S-100 protein. The observed/ expected death ratio was markedly increased with increasing levels of S-100 beta (P < 0.001). A fivefold increase in relative hazard was indicated by a value of S-100 beta exceeding 0.6 microgram/l (P < 0.001) and when this cut-off level was used S-100 beta had additional prognostic value independent of clinical stage (P < 0.001). Our data strongly suggest that S-100 beta in serum is an independent prognostic marker that may be useful in identifying high-risk cases and monitoring response to therapy in patients with malignant melanoma.