An immunochemical and immunohistochemical study of S100 protein in renal cell carcinoma

The authors localized S100 protein in renal tubules and renal cell carcinoma by immunohistochemical study and quantitative analysis by enzyme immunoassay. The α subunit of S100 protein (S100‐α) was localized in epithelial cells of proximal tubules, thin limbs of loops of Henle, collecting tubules, and a few of Bowman's capsules. The β subunit (S100‐β) was immunostained in the distal tubules, thick and thin loops of Henle, collecting tubules, and a few proximal tubules. In renal cell carcinoma, S100‐α was immunohistochemically demonstrated in 82% (41/50) of patients including sarcomatoid variants, whereas S100‐β was detected in 46% (23/50). Both the number of positively stained tumor cells and the staining intensity were greater in S100‐α than in S100‐β. Concentrations of S100‐α in the cortex were 80.3 ± 22.5 ng/mg protein (n = 7), whereas those of renal cell carcinoma were 387 ± 533 ng/mg protein (n = 19), i.e., about five times higher. Concentrations of S100‐β in both normal kidney (1.96 ± 0.74 ng/mg protein) and renal cell carcinoma (2.05 ± 2.16 ng/mg protein) were much lower than those of S100‐α. The authors also localized S100‐α and S100‐β in tissues of other renal tumors and tumors arising from other organs. S100ao appears to be a useful immunohistochemical marker for renal cell carcinoma.