Lung cancer is not contagious. Patients suffering from tuberculosis are called open tuberculosis when they have positive sputum bacteria and are contagious, so patients who encounter coughing and coughing with blood in sputum should pay attention to prevent the disease. Unlike tuberculosis, lung cancer is a malignant tumor with abnormal cell proliferation and loss of normal cell shape and dynamics under the effect of many different carcinogenic factors. Cancer cells excreted through sputum are rapidly denatured and necrotic due to the evaporation of sputum water, etc. Even fresh sputum needs to be given various nutrients and specific conditions in order for cancer cells to grow and multiply outside the body. Scientists often need to go through a lot of hard work in order to cultivate a living cancer cell to succeed, so cancer is not contagious. In animal experiments, tumor-bearing animals were kept together with non-tumor-bearing animals for a long time, and no direct transmission was found. Some families have more than one person getting lung cancer or other tumors in succession, which may be related to the fact that the same family members have common genes and they may be in the same cancer-causing environment. For example, smoking, exposure to radioactive substances, etc., so the same family members can successively develop malignant tumors.