These membrane-bound proteins, particularly members like P-gp (ABCB1), MRP1 (ABCC1), and BCRP (ABCG2), play pivotal roles in the efflux of doxorubicin and other chemotherapeutic agents out of cancer cells, thereby reducing intracellular drug concentrations and diminishing the efficacy of the treatment. The gene discussed is ABCG2; the disease is cancer.