To gain greater insight into the biological mechanisms occurring shortly after discontinuation of VEGFR TKIs treatment because of progressive disease (PD).Sixteen patients with PD during treatment with sorafenib or sunitinib were randomized to either directly stop the VEGFR TKI or to continue for another two weeks. At baseline (i.e. at the moment of PD) and after two weeks FDG-PET/CT, functional-MRI and blood biomarkers of disease were evaluated.A statistically significant difference in median change from baseline to two weeks later in K(trans) and LDH levels was observed between patients who directly stopped versus those who continued treatment (1.6 s(-1) versus -1.1s(-1), p=0.03; -73.0 U/L versus 52.0 U/L, p=0.008; respectively). There were no further differences between groups.Two weeks after discontinuation of VEGFR TKIs in mRCC because of PD, a rise in K(trans) accompanied by a decrease in LDH indicates an increase in tumor vascularization. This implies that at the moment of PD the effect of VEGFR TKIs is not completely exhausted.