ABL1 and chronic myelogenous leukemia, BCR-ABL1 positive: BMI1, a major component of the polycomb repression complex (PRC) type 1.4, is upregulated in patients with advanced stages of BCR-ABL-induced chronic myelogenous leukemia (CML)8 and through its repressive activity on the Cdkn2a locus18 and other less well-characterized activities results in leukemic transformation19.