CDKN2A and osteosarcoma: Saos‐2‐B‐Luc/mKate2‐CDX does not express the TP53 gene exhibits RB1 mutation and normal CDKN2A, whereas HOS‐Luc/mKate2‐CDX is TP53 mutated and has CDKN2A homozygous deletion 11, 18, hallmarks of aggressive osteosarcoma.