The reciprocal translocations t(8;21)/AML1-ETO, t(15;17)/PML-RARA, and inv(16)/CBFB-MYH11 are characterised by distinct morphologic phenotypes and by a favourable prognosis; reciprocal translocations involving the MLL gene on 11q23 are, by contrast, associated with poor prognosis and are frequent in therapy-related AML (t-AML). This evidence concerns the gene CBFB and acute myeloid leukemia.