One of the main mechanisms by which cancer cells become resistant is up-regulation of various ABC transporters such as P-glycoprotein (P-gp), Breast Cancer Resistant Protein (BCRP) and Multidrug Resistant Protein 1 (MRP1) which efficiently remove the drug from the cell, thus causing the drug to lose its effect [3]. The gene discussed is ABCG2; the disease is cancer.