FOXO1 and embryonal rhabdomyosarcoma: Although compelling, these results alone are not definitive evidence, because GSK3β may affect other non-PAX3-FOXO1-related biological pathways, as was demonstrated for the translocation-negative embryonal rhabdomyosarcoma.24 However, we found that directly inhibiting phosphorylation at Ser201 through mutational analysis, which removes phosphorylation of the fusion protein independent of GSK3β action, reduces migration, invasion and proliferation (Figures 2, 3 and 4), and inhibiting phosphorylation at Ser205 reduces proliferation and anchorage-independent growth (Figures 4 and 5).