For many years, treatment of acute promyelocytic leukemia (APML) with retinoic acid and arsenic trioxide was the prime example for a successful intervention based on differentiation processes, but at present degradation of the PML-RARA oncoprotein but not cellular differentiation per se is assumed to be the major mechanism to eradicate APML [11]. This evidence concerns the gene RARA and acute promyelocytic leukemia.