Selenium supplementation is not effective in treating lung cancer. Selenium is an essential trace element that participates in the normal metabolism of the human body. The human body cannot synthesize selenium on its own, and can only rely on food and selenium supplements to obtain it. Adequate supplementation of selenium can improve the immune ability of the body. For those who have already consumed enough selenium, supplementation of selenium cannot produce beneficial effects, and excessive supplementation can be harmful to the body. Lung cancer is a malignant tumor disease with high incidence rate, which seriously endangers health. At present, clinical treatment of lung cancer is mainly through surgery, radiotherapy, targeted therapy and other methods. Whether selenium supplementation is useful for lung cancer depends on the level of selenium in the body before selenium supplementation. Selenium supplementation will have positive effects on some specific lung cancer patients, but selenium supplementation does not have the effect of treating lung cancer. Lung cancer patients should use scientific and reasonable treatment under the guidance of doctors, and should not blindly take selenium supplementation on their own, which will have adverse effects on their body.