BCR-ABL1 acute myeloid leukemia: clonal selection of a BCR-ABL1(-) subclone as a cause of refractory disease with nilotinib treatment

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). Here, we report the first case in which a dominant Philadelphia chromosome-positive subclone was detected upon relapse in a formerly Philadelphia chromosome-negative MLL-AF6(+) AML. Due to refractory disease under salvage chemotherapy, the patient was started on nilotinib treatment. As a result, the Philadelphia chromosome-positive subclone was eradicated within 1 month; however, disease progressed and was again dominated by the Philadelphia chromosome-negative founding clone, demonstrating rapid clonal expansion under nilotinib-induced selection pressure.