This is supported by cytogenetic and molecular findings: for example, CLL cells in such cases typically lack the Philadelphia chromosome or BCR::ABL1 fusion seen in CML, and conversely, the myelogenous cells do not carry CLL-specific immunophenotypic markers or immunoglobulin gene rearrangements. This evidence concerns the gene ABL1 and chronic myelogenous leukemia, BCR-ABL1 positive.