The resulting persistence accumulation and mutations could lead to progression of disease as has been seen in chronic myeloid leukemia, where EVI1 synergizes with the pre-existing oncogene (such as BCR-ABL) to give a highly proliferating and aggressive leukemic clone in a subgroup of CML patients that progresses to blast crisis. This evidence concerns the gene ABL1 and chronic myelogenous leukemia, BCR-ABL1 positive.