The peroxiredoxin (PRX) family comprises six antioxidant proteins, PRX I, II, III, IV, V and VI, which protect cells from reactive oxygen species (ROS) by preventing the metal-catalyzed oxidation of enzymes. The PRX proteins primarily utilize thioredoxin as the electron donor for antioxidation, although they are fairly promiscuous with regard to the hydroperoxide substrate. In addition to protection from ROS, peroxiredoxins are also involved in cell proliferation, differentiation and gene expression. PRX I, II, IV and VI show diffuse cytoplasmic localization, while PRX III and V exhibit distinct mitochondrial localization. The human PRX IV gene is expressed in many tissues. It exists as a precursor protein, which is only detected in testis, and aprocessed secreted form. PRX IV is highly expressed in lung cancer and is necessary for the promotion of lung cancer in vitro. Studies have demonstrated that PRX IV positive expression is significantly correlated with recurrences and shorter disease-free survival in patients with early-stage lung squamous cell carcinoma, and therefore can be used as a prognostic marker in lung squamous cell carcinoma.