BCR and chronic myelogenous leukemia, BCR-ABL1 positive: Chronic myeloid leukemia (CML) is a myeloproliferative disorder that results from the reciprocal translocation of the ABL1 oncogene on chromosome 9 with the breakpoint cluster region (BCR) gene on chromosome 22 [t(9; 22)], leading to the formation of the BCR-ABL oncoprotein.