This may simply be because clinical studies of ABCB1 inhibitors did not routinely include molecular characterization of ABCB1 expression status in tumour tissues, which is a major issue since only a small fraction of cancers will express ABCB1 at functional levels capable of conferring drug resistance, and thus be expected to gain benefit from an ABCB1 inhibitor (Robey et al., 2018). The gene discussed is ABCB1; the disease is cancer.