ABCG2 and cancer: Several of them, such as P-glycoprotein (P-gp), multidrug resistance protein 1 (MRP1), and breast cancer resistant protein (BCRP), are highly expressed in drug-resistant cancer cells to mediate the efflux of drugs, thereby conferring drug resistance ability to cancer cells (Mao and Unadkat, 2015; Domenichini et al., 2019; Muriithi et al., 2020).