High concentrations of ATO induced apoptosis in APL cells, while low concentrations induced differentiation, and ATO induced apoptosis in NB4 cells through the downregulation of Bcl-2 expression and regulation of the PML-RAR alpha/PML protein (Chen et al., 1996; Zhao et al., 2001). This evidence concerns the gene BCL2 and acute promyelocytic leukemia.