S-100 protein serum levels in patients with benign and malignant diseases: false-positive results related to liver and renal function.

S-100 serum concentrations were analyzed in 39 healthy people, 130 patients with benign diseases and 304 patients with malignancies, including 49 patients with locoregional diseases and 255 with advanced diseases. S-100 was determined by a commercial immunoluminometric assay, and 0.20 ng/ml was considered to be the upper limit of normality. In none of the healthy people was S-100 higher than 0.2 ng/ml. Slightly high S-100 concentrations were found in 33 out of 130 patients (25%) with benign diseases (mean 0.21 +/- 0.45 ng/ml). Significantly higher S-100 serum levels were found in patients with liver cirrhosis (63%, 10/16) (p = 0.024) or renal failure (45%, 8/18) (p = 0.03) than in patients with other benign diseases or in healthy people. Abnormal S-100 serum levels were found in 68 of the patients (22.5%) with malignancy (mean 1.01 +/- 5.9 ng/ml). The highest S-100 concentrations were found in patients with malignant melanomas (p = 0.001). Excluding melanoma patients, the S-100 serum levels in patients with malignancies were not related to tumor origin or stage but were clearly related to the site of metastasis, with patients with liver metastases showing higher values than patients with metastases without liver involvement (p = 0.02). No statistical differences were found among patients with liver cirrhosis, primary liver cancer or liver metastases. In conclusion, S-100 is a useful marker for melanoma, but abnormal levels of this tumor marker may be found in benign and malignant diseases associated with liver or renal injury. Copyright 2002 S. Karger AG, Basel