MLL-PTD is associated with 5–10% of AML with normal karyotype and 25% of these patients also carry a FLT3 (FMS-like tyrosine kinase 3) internal tandem duplication (FLT3-ITD) mutation, suggesting that MLL-PTD requires cooperating mutations to produce AML [123,124]. This evidence concerns the gene BCS1L and acute myeloid leukemia.