Acute promyelocytic leukemia (APL) is characterized by distinct clinical and biological features and by the reciprocal translocation t(15;17)(q22;q21)in the majority of patients. The translocation generates the fusion of the promyelocytic leukemia (PML) gene to the gene for retinoic acid receptor alpha (RARA) and these patients are responsive to differentiation treatment with all-trans retinoic acid (ATRA). Rare cases of patients with a morphological diagnosis of APL have variant chromosome translocations, which fuse RARA gene with partner genes other than PML, such as in the variant translocation t(5;17)(q35;q21) that fuses the N-terminus of nucleophosmin (NPM1) gene at 5q35 to the retinoic acid receptor alpha at 17q21....