Rising levels of serum S100 protein precede other evidence of disease progression in patients with malignant melanoma

BACKGROUND: Several serum markers may be useful in the detection of metastatic melanoma, but none is in routine clinical use. OBJECTIVE: To assess the validity of S100 protein as a serum marker of melanoma progression. METHODS: Serum S100 protein levels were measured in 496 serum samples from 214 melanoma patients, using the Sangtec luminescence immunoassay. There were 75 patients with stage 1 melanoma, 66 initially with stage 2 melanoma, 49 initially with stage 3 melanoma and 24 with stage 4 melanoma. RESULTS: Serum S100 protein levels were < 0.2 microg L-1 in 71 of 75 (95%) stage 1 patients. One patient who had a normal level developed local recurrence. Fifty-eight of 66 (88%) stage 2 patients also had normal serum S100 protein levels. One with elevated levels progressed to stage 3 melanoma and five with elevated levels progressed to stage 4 disease. The remaining two with elevated serum S100 protein remained well. Thirty-five of 49 (71%) stage 3 patients had normal levels and, of these, two have progressed to stage 4 disease. Three patients with stage 3 disease had an elevated serum S100 protein level on one occasion but remained well. Eleven of 13 patients who developed stage 4 melanoma during the study had rising levels of serum S100 protein > 0.2 microg L-1 5-23 weeks before detection of melanoma progression by conventional means. Twenty-two of 24 patients with stage 4 disease throughout the study had consistently elevated serum S100 protein levels, and the two patients with normal levels were clinically disease free after surgery and chemotherapy. None of 14 control subjects with atypical naevi had elevated S100 protein levels, and only one of 11 healthy normal controls had an elevated level. CONCLUSIONS: Thus, rising levels of serum S100 protein are a specific and sensitive clinically relevant marker of tumour progression in melanoma patients, which precedes other evidence of melanoma recurrence.