PGP and cancer: It has been proposed that cancer cells develop multiple mechanisms that eventually impair drug uptake by the cells, for example, changes in lipid plasma membrane composition, downregulation of the expression of drug transporters that promote drug uptake by the cell and overexpression of efflux pumps that expel drugs out of the cells such as ATP-binding cassette pumps (e.g., P-glycoprotein, P-gp) [24].