The observed differences between IDH mutated chondrosarcomas versus IDH mutated gliomas on DNA and histone modifications, is likely attributable to additional genetic alterations that cooperate with mutant IDH to initiate cancer, e.g. ATRX and TP53 mutations in IDH mutant gliomas and COL2A1, YEATS2, NRAS, TP53, Rb- and Hh- signaling mutations in chondrosarcomas [47, 51–53]. This evidence concerns the gene RB1 and central nervous system cancer.