In this context, it is interesting to note that expression of the main targets of the drugs described in this review, VEGFR, PDGFR, FGFR, c-KIT, RET, MET and AXL, is reasonably well-documented for OS and ES patients, with the vast majority of patients presenting some level of protein expression (4, 68). This evidence concerns the gene KIT and Ewing sarcoma.