The datasets and computer code produced in this study are available at the ArrayExpress database with the following accession number: RNA Affymetrix GeneChip: E‐MTAB‐11743 (Title: Alternative Lengthening of Telomeres (ALT) and ATRX inactivation in high‐grade pediatric osteosarcomas. This evidence concerns the gene ATRX and osteosarcoma.