MAPK3 and neoplasm: Our results suggest that in CRC ERK1/2 inhibition may combine better with antagonists of BCL-XL than MCL1 due to their relative expression, further underlining the potential for tumour lineage-selective differences that will drive BH3-mimetic combination choices; as we show here, the ratio of pro-survival proteins will be informative in this choice, and represent a potential clinical biomarker.