Small cell lung cancer is not contagious. Small cell lung cancer is a malignant tumor, and malignant tumor and infectious disease are two completely different diseases, malignant tumor is not contagious. Infectious disease is a disease in which pathogens are transmitted from patients to healthy people through patients. Infectious disease has three elements, such as infectious source, transmission route and susceptible people. The occurrence of malignant tumor is due to the long-term effect of different carcinogenic factors, resulting in the formation of new organisms by the abnormal proliferation of tissue cells in the body. It is not because the malignant tumor is contagious, but because the members in the family have similar genetic background, living environment and eating habits, and are prone to the same kind of malignant tumor.