RB1 and osteosarcoma: Both ARMS and ERMS have simple karyotypes, whereas those of PRMS are complex, often harboring deleterious alterations in TP53, RB1, and NF1. 9,10,11 Copy-number profiles of PRMS show levels of genomic instability reminiscent of those in adult/non-translocation-driven sarcomas such as osteosarcoma.12