MCL1 and central nervous system cancer: Intriguingly, while this functionally defined dependency on BCL-XL and MCL-1 is coupled to their high RNA expression in patients and gliomaspheres28 (Supplementary Fig. 1C), this relationship did not extend to protein levels of BCL-XL and MCL-1, whose expression, along with other BCL-2 family members, was variable among patient-derived gliomaspheres and glioma patient samples (Supplementary Fig. S1D, E).