Fusion-negative sarcomas are a diverse and understudied subset of pediatric cancers. The most prevalent are embryonal rhabdomyosarcoma (ERMS) and osteosarcoma (OS). Osteosarcoma is characterized by an abnormal genome with many alterations, most of which are called “copy number gains” or “copy number losses.” In a normal genome, there are only two copies of every gene. However, in OS many genes have more than 4 copies, sometimes even 10 or more copies.
