MCL1 and breast cancer: Whilst the pro-tumor role of MCL-1 in models of breast cancer is highly reliant on BH3-dependent functions of MCL-1, there may be important non-apoptotic roles for MCL-1 in tissues outside the breast and the ability of MCL-1-targeting strategies to impact or spare these alternative functions must be considered given the fatality of complete Mcl1 deletion in mice [6,118,131].