Zhang and colleagues64 observed that regorafenib improves BCRP-overexpressing S1-M1-80 CRC cells sensitivity to mitoxantrone and SN-38, both substrates of BCRP, due to its interaction with the BCRP transmembrane domain and its ability to impair BCRP efflux and increase intracellular drug retention. The gene discussed is ABCG2; the disease is colorectal carcinoma.