ROS up-regulation induced by chemotherapy drugs exposed tumor cells to oxidative stress, oxidative damage provoked the overexpression of the PPP rate-limiting enzyme glucose-6-phosphate dehydrogenase (G6PD), accelerated PPP enhanced the production of nicotinamide adenine dinucleotide phosphate (NADPH), thereby up-regulating the synthesis rate of the antioxidant glutathione (GSH). The gene discussed is G6PD; the disease is neoplasm.