During the consultation and treatment of patients, family members often ask: Is this cancer contagious? What should chaperones pay attention to in the process of patient care? In clinical practice, cancer is not treated as an infectious disease, and no hospital in the world isolates cancer patients for treatment. There are no reports of mutual transmission between cancer patients and other patients, relatives and medical staff, nor is there a large-scale epidemic of cancer in the same area at the same time like an infectious disease. Therefore, cancer is not a contagious disease. However, in real life, we sometimes see multiple people in the same family suffering from the same disease at the same time or successively, which is mostly seen in liver cancer or colorectal cancer, etc. What is the reason? From the medical point of view, the important cause of liver cancer is hepatitis B virus infection, and hepatitis B virus is contagious, so the same family may have hepatitis B infection because of eating together, which may lead to liver cancer at the same time or successively. Colorectal cancer, on the other hand, may be caused by similar dietary habits, lifestyle and genetic qualities of the same family, such as high-calorie diet, which predispose to the same cancer. Therefore, the occurrence of the same tumor in the same family or household does not indicate that the cancer is contagious. However, it should be noted that some cancers are accompanied by infectious diseases that cause cancer, such as hepatitis B. Family members and companions need to prevent contagion when they come in contact with the patient. Meanwhile, if a liver cancer patient is found to carry hepatitis B virus at the same time, family members should have a physical examination to check the hepatitis B 2:30, and if they carry it, they should treat it in time, and if they do not carry it, they need to take preventive injection to prevent it.