MCL1 and chronic myelogenous leukemia, BCR-ABL1 positive: MCL1 expression can be upregulated in CML cells either by BCR-ABL1 signaling [9] or potentially by the microenvironment, mainly through signaling of the cytokine receptors which play an important role in the TKI resistance of CD34+ CML stem/progenitor cells [35, 36].