Heterogeneous MCL-1 dependence has been observed in non-small cell lung cancer lines, AML, chronic myelogenous leukemia, B-cell acute lymphoblastic leukemia (B-ALL) and MM.66, 98, 99, 100, 101 MCL-1 inhibition may have side effects like hematopoietic toxicity102 cardiotoxicity103 and perhaps affect mitochondrial respiration.104 However, it remains to be seen the extent to which titratable MCL-1 inhibition by drugs in humans phenocopies gene deletion in mice. Here, MCL1 is linked to B-cell acute lymphoblastic leukemia.