Innate or upregulated expression of ABCB1 has been identified as an important clinical factor in the treatment of several cancers, first reported in leukaemias [5,6] breast cancer [7], small-cell lung cancer [8], (reviewed in Fletcher et al. 2016 [9] and Robey et al. 2018 [10]). Here, ABCB1 is linked to cancer.