MCL1 and neoplasm: Briefly, by exposing a single-cell suspension of tumour cells to pro-apoptotic BH3-only peptides that have specific affinities for various anti-apoptotic BCL-2 family proteins (e.g., MCL-1, BCL-XL and BCL-2), both a tumour’s dependency on an apoptotic block(s) and the overall apoptotic potential for cell death (i.e., mitochondrial priming) can be assessed23.