In addition to its ability of conferring multidrug resistance in cancer cells, P-gp is highly expressed in normal organs important for the absorption (the small intestine), elimination (the liver and kidney) and distribution (e.g., the placental and blood-brain barriers) of drugs and xenobiotics, and has been recognized as one of the most important drug transporters that are involved in clinically relevant drug disposition and drug-drug interactions [6]. The gene discussed is PGP; the disease is cancer.