SOD2 and lung cancer: In this study, it was not possible to control all factors influencing serum total SOD activity or SOD1 and SOD2 concentrations—for example, diet, lifestyle, and clinical parameters—therefore, further studies should be performed in a more homogenous group of lung cancer patients, or analyses should also be adjusted for the aforementioned data in order to better evaluate the impact of circulating enzymes on the prediction of mortality in lung cancer patients.