PGP and neoplasm: P-glycoprotein (P-gp), an important efflux transporter with ‘drug pump’ function, can bind to drug molecules and pump drug molecules out of tumor cells, reducing the concentration of drugs in tumor cells to induce multidrug resistance of tumor cells, which is one of the most important mechanisms for tumor cells to produce multidrug resistance (Wu et al., 2016; Ge et al., 2017).