ABL1 and chronic myelogenous leukemia, BCR-ABL1 positive: In both children and adults, a hematopoietic stem cell has acquired the BCR::ABL1 fusion gene and breakpoints occur in the same major breakpoint cluster regions (M-BCR) in the BCR gene on chromosome 22, but in chronic-phase CML the breakpoint distribution in BCR has been shown to be different in children [7].