Data supporting this assumption are still missing; nevertheless, the recently published paper of Zavada et al (2003) demonstrating elevated CA IX ECD in the serum of patients with renal cell carcinomas, which frequently upregulate CA IX due to inactivating mutation of VHL tumour suppressor gene and constitutive activation of HIF-1, suggests that the idea is meaningful. This evidence concerns the gene CA9 and hereditary clear cell renal cell carcinoma.