To determine whether disease observed with BCR-ABL and MSI2-HOXA9 was more aggressive because it was more undifferentiated than disease driven by BCR-ABL alone, we compared the BCR-ABL/MSI2-HOXA9 leukemic cells to the previously established model of blast crisis CML driven by BCR-ABL/NUP98-HOXA9 (Dash et al. 2002). Here, HOXA9 is linked to chronic myelogenous leukemia, BCR-ABL1 positive.