ABL1 and leukemia: The fact that some BCR-ABL+ cases are not sensitive to imatinib nor nilotinib and that some BCR-ABL– cancer cells are still killed by imatinib or nilotinib suggests the existence of additional pathways regulated by BCR-ABL in leukemia cell growth, and multiple mechanisms of action of imatinib and nilotinib in inducing cancer cell apoptosis.