While FoxO1 is required for vasculogenesis,16, 17 FoxO3 plays a critical role in ovarian primordial follicle activation.17, 18 FoxO4-null mice exhibit increased intestinal epithelial permeability and are susceptible to trinitrobenzene sulfonic acid (TNBS)-induced colitis.19 In the context of cancer, it remains controversial whether FOXOs act as bona fide tumour suppressors. This evidence concerns the gene FOXO4 and cancer.