Blood levels of carbonic anhydrase 9 correlate with clear cell renal cell carcinoma activity

Introduction: Biomarkers for early detection of renal cell carcinoma (RCC) may help diagnose minimal residual disease in patients at risk for RCC, can guide anti-angiogenic therapy, or may help identify candidates for adjuvant treatment. In this study, we investigated whether blood levels of carbonic anhydrase 9 (CA9) correlate with RCC tumor burden and therefore disease activity. Methods: CA9 is a von Hippel-Lindau-hypoxia inducible factor target upregulated in clear cell RCC. We used an anti-CA9 antibody (M75)-based enzyme-linked immunosorbent assay test to measure CA9 levels in blood obtained before and after nephrectomy for clinically localized disease in patients with: (1) clear cell RCC, (2) papillary and chromophobe RCC or oncocytoma, or (3) benign kidney lesions, and we compared these samples to blood drawn from normal control individuals. Results: We observed a significant (p∈<∈0.006) decrease in the blood levels of CA9, after nephrectomy for localized disease, in the majority of patients with clear cell RCC (57%). In contrast, patients with nonclear cell RCC, benign disease, or those having undergone debulking nephrectomy for metastatic disease did not have a decrease in CA9 blood levels after nephrectomy. Preliminary longitudinal follow up measurements of CA9 levels in a small group of patients indicated that rising CA9 levels may correlate with disease progression. Conclusions: Plasma CA9 levels correlate with disease activity in a subset of clear cell RCC patients and should be considered in future multiplex RCC biomarker development algorithms. © 2008 Humana Press.