CBFB gene break apart is a characteristic chromosomal abnormality of AML, accounting for 5%-10% of total AML patients and 23% of M4 patients It is usually found in the AML-M4E0 subtype, but less in M2, M5 and M4 (no eosinophilic granulocytosis). It is now considered that CBFB gene break apart is a characteristic genetic alteration of M4E0.