 The presence of a Philadelphia chromosome with a corresponding BCR-ABL1 rearrangement is the hallmark of chronic myeloid leukemia, but is considered a very rare event in de novo acute myeloid leukemia (AML).     ///    BCR-ABL1(+) acute myeloid leukemia: clonal selection of a BCR-ABL1(-) subclone as a cause of refractory disease with nilotinib treatment.. 