As revived by Zhang et al., numerous reports of drug resistance in patients emphasized the upregulation of MRP proteins in vast numbers of cancers: MRP1, MRP4 and MRP8 in breast cancer; MRP1-4 in lung cancer; MRP1–3 in non-small cell lung cancer; MRP1 in pancreatic cancer; MRP1 and MRP4 in kidney cancer; and MRP1, MRP2, MRP4, MRP6 and MRP8 in colorectal cancer [28]. Here, ABCC4 is linked to colorectal cancer.