The fresh sputum coughed up by lung cancer patients sometimes contains a small amount of cancer cells, but the small amount of cancer cells will rapidly degenerate and necrotize when they are separated from the body’s nutrition and specific environment. However, unlike other viruses and bacteria that can spread to others, the so-called contagion is generally for infectious diseases. Simply put, a certain disease is transmitted from one person to another through a certain way, but such diseases are caused by pathogens, which can be transmitted from one person to another, from animal to animal or from human to animal.