ABCB1 and cancer: The first known mechanism is overexpression of the MDR-1 gene encoding P-glycoprotein in taxol-resistant cancer cells.2 P-glycoprotein functions as a drug-efflux pump on the surface of cancer cell to efflux taxol.3 Other mechanisms responsible for taxol resistance include the mutations of taxol-binding protein tubulin, deregulation of cell cycle and high expression of anti-apoptotic protein.4