RET and osteosarcoma: Molecular analysis may be useful in the case of histological types with a low response rate to conventional chemotherapy, such as osteosarcomas: several in vitro and preclinical studies showed the expression of platelet-derived growth factor receptors (PDGFRs), VEGFRs, and RET in osteosarcomas; thus, multi-kinase inhibitors can be evaluated as future potential therapeutic tools [122,123].