ATRX and osteosarcoma: Consistent with the amplification of the gene, TOP3A mRNA was overexpressed in the ALT‐positive tumors overall and in the ALT‐positive ATRX‐wt tumors but not in the ALT‐negative or ALT‐positive ATRX‐mutated tumors (Fig 4B), strengthening the point that TOP3A overexpression and ATRX mutation are exclusive genomic events in ALT‐positive osteosarcomas.