FOXO1 and embryonal rhabdomyosarcoma: Alveolar RMS is commonly driven by the fusion of PAX3 or PAX7 to the FOXO1 gene (PAX3/7::FOXO1; ie, fusion-positive).2,3 In contrast, ERMS typically lacks the canonical PAX3/7::FOXO1 fusion (ie, fusion-negative); these tumors are typically driven by somatic mutations in the RAS signaling pathway,4,5 loss of heterozygosity at 11p15.5,6 and whole chromosomal alterations.7