Acute promyelocytic leukemia (APL), the main subtype of acute myeloid leukemia in which positive responses are observed after treatment with ATRA [56], is characterized by chromosomal translocations involving the RA receptor-α (RARA) gene that result in clonal expansion of hematopoietic precursors blocked at the promyelocytic stage of differentiation [40]. The gene discussed is RARA; the disease is acute myeloid leukemia.