These include changes in apoptotic pathways, increased DNA damage repair, drug inactivation, alteration of drug targets and increased expression of ABC transporters, able to pump xenobiotics (such as toxins or drugs) out of cells.1 Many cancer cells express large amounts of MDR1 (ABCB1, or P-glycoprotein 1), which confers them MDR.2, 3, 4. The gene discussed is ABCB1; the disease is cancer.