In the past, everyone thought that “lung disease” was contagious, and this “lung disease” was tuberculosis. Patients suffering from tuberculosis are called open tuberculosis when they have positive sputum bacteria and are contagious, so patients who cough and cough with blood in their sputum should pay attention to prevention. Tuberculosis is a disease transmitted through the respiratory tract, while lung cancer is different from tuberculosis. Cancer cells excreted through sputum are rapidly denatured and necrotic due to 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.