Abstract: The invention relates to a novel approach for the diagnosis and therapy of renal cell carcinoma, and other renal tumors, for example Wilms' tumor or other tumors not originating from the kidney or non-malignant kidney pathologies. The areas of application of the invention include the field of medicine and the pharmaceutical industry but also basic biology. The aim of the invention is to provide novel forms of treatment which are urgently required regarding the present state-of-the-art in treatment of renal carcinoma and other cancers. It was discovered that the Nbk protein which is highly expressed in normal renal tissue, is either not expressed at all or only weakly expressed in the tumor tissue. The protein expression and the loss of Nbk was examined in renal cell carcinoma samples by the use of immunohistochemistry, PCR strategies, mutation and deletion analyses.