ABL1 and chronic myelogenous leukemia, BCR-ABL1 positive: Chronic myeloid leukemia (CML) is a myeloproliferative neoplasm caused by a fusion gene that encodes for the oncoprotein BCR-ABL, with constitutive tyrosine kinase activity (1); the target for tyrosine kinase inhibitor(s) [TKI(s)] (2).