Embryonal rhabdomyosarcoma (ERMS) is the most common pediatric soft tissue sarcoma, and its incidence is significantly increased in children with Costello syndrome (CS), a rare genetic disorder resulting from heterozygous germline mutations in the proto-oncogene HRAS located on 11p15.5 (1–5). The gene discussed is HRAS; the disease is embryonal rhabdomyosarcoma.