Over the last decade there has been a growing interest in the therapeutic potential of As2O3 as either single agent or in combination with ATRA for successful treatment of Acute Promyelocytic Leukemia (APL) patients.22,23 Awareness of such ethnic variations in the distribution of this polymorphism, characterization of AS3MT gene and the utilization of pharmacokinetic testing for the identification of different AS3MT alleles in patients may provide a useful tool for optimizing therapy and side-effects for the individual patient. Here, AS3MT is linked to acute promyelocytic leukemia.