TP53 and osteosarcoma: In contrast to other malignancies carrying H3F3A mutations, as for example pediatric glioblastoma with co-occurring mutations in tumor protein 53 (TP53) and ATRX9,20 (Fig. 1e, Supplementary Fig. 1g), and to other bone tumors, e.g., osteosarcoma (Fig. 1f, Supplementary Fig. 1h, i), GCTB showed an extremely low overall mutation frequency for H3.3 MUT and H3.3 WT cells (Fig. 1f, Supplementary Fig. 1e, f).