KDR and fibrosarcoma: Previous studies have demonstrated that the drug efflux function of P-gp and ABCG2 could alter the bioavailability, distribution and efficacy of epidermal growth factor receptor (EGFR) inhibitors [57,58,59], vascular endothelial growth factor receptor (VEGFR) inhibitors [60], rapidly accelerated fibrosarcoma (RAF) inhibitors [61,62,63,64], PARP inhibitors [65,66,67], and ALK inhibitors [68,69,70,71].