Serum Carbonic Anhydrase 9 (CA9) Level as Biological Marker of the Treatment Response in Metastatic Renal Cell Cancer : a Pilot Study

One third of patients with kidney cancer are diagnosed in the metastatic stage, and among patients with a localized form, about 30 to 40% will develop metastases after surgery.

Medical treatment of metastatic renal cancer include immunotherapy with interferon α and/or IL-2, or targeted therapies such as anti-angiogenic (anti-vascular endothelial growth factor (VEGF), anti-tyrosine kinase inhibitors and m-TOR). These treatments sometimes associated (or IL2 + INF or INF AntiVEGF) do allow for objective response in 15 to 30% of cases (net benefit of targeted therapies), but are carriers of potentially significant side effects and are very expensive. The treatment response is considered on imaging exams repetitive, costly and inconsistently reliable. A serum marker of tumor development would be particularly welcome.

CA9 is an oncogene also know as CA IX, carbonic anhydrase 9 or MN/CA9. The gene encoding an oncoprotein called indifferently membrane antigen MN, MN/CA9 isoenzyme, carbonic anhydrase IX CA9, G250/MN/CA9 or protein G250. It was demonstrated that the level of expression of CA9 in tumor tissue can be used as a predictive marker of response to immunotherapy.

In previous studies, the investigators tried to use CA9 to improve the differential diagnosis of kidney tumors using tumor biopsy or fine needle aspiration. More recently, the investigators have developed the ELISA and quantitative reat time polymerase chain reaction (RT-PCR) to study the CA9 protein and CA9 mRNA in the serum of patients with non-metastatic kidney cancer. The investigators have thus shown that CA9 was overexpressed prior to surgery and that this expression disappeared after tumor ablation.