Besides, drug resistance may also be a result of the inactivation of drugs caused by detoxifying enzymes expressed in cancer cells, such asase I enzymes- NAD(P)H-quinone oxidoreductase 1 (NQO1), and phase II enzymes-placental (P) isoform of glutathione-S-transferase (GSTP1). The gene discussed is NQO1; the disease is cancer.