CDK4 and osteosarcoma: For example, IDH1/2 mutations are the molecular feature to distinguish chondrosarcoma from osteosarcoma (36), the high frequency of MDM2 and CDK4 amplifications in low-grade osteosarcoma (37), the high frequency of NCOA2 fusion in mesenchymal chondrosarcoma (38), and the high frequency of H3F3A and H3F3B mutations in giant cell tumor of bone and chondroblastoma, respectively (39, 40).