RARA and acute promyelocytic leukemia: A part of relapsed and refractory APL develop resistance to ATRA and/or ATO.[18–22] Studies have found that resistance to ATRA may be related to the mutations in RARA-LBD region.[19,23] Goto et al[24] and Zhu et al[25] studied the mutations associated with targeted drugs for leukemia and believed that drug resistance of APL to ATO might be related to the mutation in the PML-B2 domain.