RAD21 and osteosarcoma: Osteosarcoma pathogenesis may involve genetic aberrations of the VEGF, mTOR, and Wnt (Wingless-related integration site) signaling pathways; inactivation of tumor suppressors p53 and Rb (retinoblastoma); and amplification of APEX1 (Apurinic/Apyrimidinic Endodeoxyribonuclease 1), MYC, CCN1 (Cellular Communication Network Factor 1), RAD21 (RAD21 cohesin complex component), AURKB (Aurora Kinase B) and CDK4 (cyclin-dependant kinase 4), RECQL4 (RecQ Like Helicase 4), RPL8 (Ribosomal Protein L8), HDMX (human homologue of Mdm2 (mouse double minute 2) proto-oncogene), and VEGFA [32,33].