Acute promyelocytic leukemia (APL) is a distinct subtype of acute myeloid leukemia (AML), defined by a balanced chromosomal translocation t(15,17) resulting in the fusion of the promyelocytic leukemia (PML) and retinoic acid receptor-α (RAR-α) genes resulting in an aberrant oncogenic protein which blocks myeloid differentiation at the promyelocyte state. The gene discussed is PML; the disease is acute promyelocytic leukemia.