While little is known about the molecular mechanisms of CIC::FOXO4 fusion oncoproteins, FOXO4 (also known as AFX) and FOXO1 (also known as FKHR) chimeras have been identified in MLL-rearranged acute leukemia (AFX::MLL) and alveolar rhabdomyosarcoma (PAX3::FOXO1) (Borkhardt et al., 1997; Sorensen et al., 2002). This evidence concerns the gene FOXO4 and rhabdomyosarcoma.