CD44 and cancer: The activity of drug transporters of the ATP-binding cassette (ABC) family such as MDR1 (Pgp-1), the ABCC family such as MRP1 and MRP2, breast cancer resistant protein family (BCRP) such as ABCG2 etc. in cancer cells leads to decrease in the intracellular concentration of the chemotherapeutic drugs by ATP-dependent efflux of unmodified drug from the cells, which contribute to drug-resistance38–41.