FOXO4 and acute leukemia: The mammalian Forkhead box O (FoxO) family includes four members expressed nearly in all tissues: FoxO1 (forkhead in rhabdomyosarcoma, FKHR), FoxO3 (forkhead in rhabdomyosarcoma like protein 1, FKHRL1), FoxO4 (acute leukemia fusion gene located in chromosome X, AFX), and FoxO6 [1].