GFI1 and chronic myelogenous leukemia, BCR-ABL1 positive: To address the question of whether the higher efficacy of palbociclib was limited to GFI1-36N homozygous cells, we also tested GFI1-36N-MLL-AF9 heterozygous cells still expressing the murine Gfi1 on one allele, as well as the human chronic myeloid leukemia (CML) cell line K562 transduced with the GFI1-36N variant.