Core binding factor (CBF) positive AML (CBFpos AML) represents 5–8% of all AMLs and is defined by the presence of a t(8;21)(q22;q22) and the associated RUNX1–RUNX1T1 fusion gene, or an inv(16)(p13.1q22)/t(16;16)(p13.1;q22) with the resulting CBFB–MYH11 fusion gene. The gene discussed is CBFB; the disease is acute myeloid leukemia.