High levels of S-100a0 (alpha alpha) protein in tumor tissues and in sera of patients with renal cell carcinoma.

The alpha alpha form of S-100 protein (S-100a0), which is distributed mainly in the heart and striated muscles, and also in the brain and kidney, was determined in tumor tissues and sera of patients with renal cell carcinoma by employing an enzyme immunoassay system for bovine S-100a0 protein. The average content of S-100a0 in the renal cell carcinoma tissue (n = 10) was about 650 ng/mg protein, 4-fold higher than that in the kidney (n = 6, 160 ng/mg protein). Immunohistochemically, S-100a0 antigen was localized in such epithelial cells as proximal tubules, Bowman's capsules and collecting tubules of normal kidney, and in the cytoplasm, nucleus and occasionally plasma membrane of the tumor cells. The contents of S-100a0 protein in various lung carcinoma tissues were low (less than 10 ng/mg protein). Serum S-100a0 concentrations were less than 0.3 ng/ml in healthy subjects, but they were significantly increased in patients with renal cell carcinoma at diagnosis, showing greater than 0.5 ng/ml in 17/32 cases (53%). Serum S-100a0 levels were also enhanced in some patients with lung cancer (10/33, 30%), breast cancer (4/20, 20%) and other non-neoplastic diseases, indicating that S-100a0 protein in the serum is not a specific biomarker for renal cell carcinoma. However, serum S-100a0 concentrations in patients with renal cell carcinoma changed in parallel with the clinical course during treatment. These results suggest that serum S-100a0 may be a useful biomarker at least for monitoring the clinical course of renal cell carcinoma.