MT-ND6 and neoplasm: To study the role of mitochondrial ND6 gene nonsense and missense mutation in the regulation of cell migration and invasion, we further investigated the cellular ROS level, since it was reported that defective activity of NADH dehydrogenase could induce the increase of ROS [7-9] and the level of ROS is relevant to tumor cell migration, invasion and metastasis [11,19].