In acute promyelocytic leukemia, the promyelocytic leukemia–retinoic acid receptor (RAR)α fusion protein binds the corepressor NCOR2 with abnormally high affinity, thereby repressing differentiation genes even in the presence of physiological levels of the RARα ligand all trans retinoic acid (32, 33). This evidence concerns the gene NCOR2 and acute promyelocytic leukemia.