The latter has been repeatedly implicated in drug-resistant solid cancers; e.g., in retinoblastoma [35], bladder cancer [36] and colorectal cancer [37], in which the heightened drug-efflux activity could be functionally linked to FOXM1-dependent upregulation of ABCC4, ABCG2 and ABCC10, respectively. Here, ABCG2 is linked to retinoblastoma.