The primary objective of the study is to evaluate the feasibility of 89Zr-bevacizumab PET imaging as a biomarker before and during treatment with sunitinib or bevacizumab plus interferon in patients with RCC. 89Zr-bevacizumab PET imaging will be regarded a promising biomarker if the target for treatment (VEGF) can be visualised and if uptake changes after institution of treatment.