The P-gp transporter and MDR-associated proteins, MRP1 and ATP binding cassette subfamily C member 1 (ABCC1), are particularly relevant to cancer chemotherapy, as are the breast cancer resistance proteins, BCRP and ABCG2, which are encoded by GTPase-activating protein MDR1 (MDR1) genes [365]. The gene discussed is ABCG2; the disease is breast cancer.