IDH1 and osteosarcoma: Osteosarcomas and chondrosarcomas are characterized by a complex and variable genomics, where only few genes, such as TP53, RB, ATXR or PTEN in osteosarcomas [3,4,5] and IDH1/2, COL2A1 or TP53 in chondrosarcoma [6,7], were commonly mutated in a significant number of patients.