ABCB1 and cancer: Several studies found that the mechanism of HCC drug resistance is complicated, and probably is a combination of two aspects: on one hand, drug delivery to cancer cells is impaired, which generally results from overexpression of ATP-binding cassette (ABC) transporters such as P-glycoprotein (P-gp); on the other hand, drug sensitivity is affected by various changes in drug resistant cancer cells, including increased repair of DNA damage, reduced apoptosis, and altered metabolism of drug3, 4, 5.