ABCB1 and cancer: Chemoresistance of cancer is often mediated by ABC transporters.15 Of the 48 human ABC transporters, ABCB1, ABCC1 and ABCG2 are most often associated with multidrug resistance.15 Other ABC transporters have been implicated in drug resistance, but these transporters have highly specialized roles in normal physiology and are less likely to have a role in drug resistance in cancer cells.