BCR and chronic myelogenous leukemia, BCR-ABL1 positive: These insertion sequences generally derived from ABL intron Ia/Ib, BCR intron 8, and other specific genes including PRDM12, SPECC1L, and MAST2. Although these inserted sequences do not participate in encoding functional protein domains, they can indirectly affect the expression level of the BCR::ABL1 fusion protein by adjusting the splice sites of the fusion gene or regulating mRNA stability, thereby leading to differences in the clinical phenotype of CML patients and their responses to drug treatment.