The observed ‘unstable CML disease’ was also seen when deletion of the Klf4 gene was induced after transformation, transplantation, and establishment of myeloid leukemia cells, which suggests that regression of leukemia was not due to differential homing of Klf4-deficient cells into bone marrow. The gene discussed is KLF4; the disease is chronic myelogenous leukemia, BCR-ABL1 positive.