Although no trials are underway, a BCL-XL-specific BH3 mimetic may well have clinical utility, as many solid tumours, especially colorectal cancer,119 have elevated BCL-XL that correlates with chemoresistance in cancer cell lines.120 Selective BCL-XL inhibitors (A-1331852, the most potent) were well tolerated in mice and modestly enhanced docetaxel efficacy against diverse solid tumour xenografts.79 As mice lacking one BCL-XL allele are healthy121 and ramped dosing can largely control the expected thrombocytopaenia,87 a therapeutic window for BCL-XL inhibition seems likely. This evidence concerns the gene BCL2L1 and colorectal cancer.