The FOXO1 gene is located on chromosome 13q14.11. The FOXO1 Break Apart FISH probe is designed to label both ends of the FOXO1 gene, respectively. A 725 Kb orange probe is designed at the 3′ end of the FOXO1 gene, and a 825 Kb green probe is designed at the 5′ end of the FOXO1 gene.

Habdomyosarcoma (RMS) is the most common pediatric soft tissue sarcoma. Main subtypes include embryonal RMS (ERMS) and alveolar RMS (ARMS). ARMS has worse prognosis and shows t(2;13) or t(1;13) translocations involving FOXO1-PAX3/PAX7 fusions in ~80% of cases.