Words of wisdom. Re: Carbonic anhydrase IX in renal cell carcinoma: implications for prognosis, diagnosis, and therapy. Stillebroer AB, Mulders PFA, Boerman DC, Oyen WJG, Oosterwijk. E Eur Urol. In press. DOI: 10.1016/j.eururo.2010.03.015.

The authors analysed the potential use and limitations of carbonic anhydrase IX (CAIX) antigen as a marker with diagnostic and prognostic value in cases of clear-cell renal cell carcinoma (ccRCC). The study reports that >95% of ccRCCs show high and homogeneous levels of CAIX expression by reverse transcription-polymerase chain reaction and immunohistochemistry. Monoclonal antibody (MAb) G250 has a high affinity for the CAIX antigen. Using MAb G250 in iodine 131-G250 radioimmunoscintigraphy (RIS) and fluorodeoxyglucose F 18 positron emission tomography (PET) can detect primary ccRCC and metastatic sites through the affinity with CAIX antigen. CAIX expression in ccRCC is also presented as a significant and independent adverse predictor of survival. Finally, CAIX has a potential role as a predictor of response to immunotherapy. Seventy-eight percent of renal cell carcinomas(RCCs) responding to interleukin-2 therapy showed high CAIX-expressing primary tumours. Similarly, CAIX expression was associated with a significantly higher treatment response rate in patients with metastatic RCC who received sorafenib.