It is a very popular misconception that cancer is contagious. In my clinical work, as an oncologist, I have been asked countless times by patients’ families: Is cancer contagious? Although they seem to be asking without thinking, in fact, they have already decided that cancer is contagious in their eyes, but they just want to get the so-called professional confirmation from me, and they are very worried about being infected by their loved ones or friends who have cancer. Why is the misconception that cancer is contagious so common? Because in our life, it seems that people in certain places or even in a certain village are particularly prone to certain kinds of cancer, and if we narrow the scope further, it seems that there is a phenomenon that many family members or couples have cancer at the same time or one after another, and they may even have the same kind of cancer. It seems that this misconception is well-founded, so it is no wonder that it is “deeply rooted” in people’s minds. Can cancer be contagious or not? The answer is obviously no! So far, it can be said with certainty that cancer itself is not contagious. Contagion means that a certain disease is transmitted from one person to another person or to some other people through some channels, that is, the contagion must meet three basic conditions, namely, the source of contagion (that is, the source of contagion, which can be human or animal), the channel of transmission (that is, the medium through which the contagion is transmitted, such as air, droplets, blood, body fluids, etc.), and the susceptibility. If any one of these three conditions is missing, then it cannot be considered as an infectious disease. Obviously, cancer does not meet these conditions at all, and there is no evidence that cancer can be transmitted directly to another person through air breathed or droplets exhaled, or blood and body fluids. However, it seems that this still cannot eliminate people’s doubts and worries, because many people think: Didn’t doctors say that many cancers are caused by viruses or even bacteria? Isn’t it confirmed in medical science that viruses and bacteria are contagious? Doesn’t this validate that cancer is contagious? It is undeniable that the occurrence of certain cancers is indeed related to certain viruses or bacteria, for example, nasopharyngeal cancer is related to EBV, hepatitis B virus is related to liver cancer, cervical cancer is related to human papilloma virus, and Helicobacter pylori is related to gastric cancer and gastric lymphoma. However, it is important to know that the above viral or bacterial infections are only related to the occurrence of certain cancers and are the cause of cancer. To say that they are contagious, at most, we can only say that these viruses or bacteria are contagious, but not the cancer itself is contagious, moreover, it is not certain that one will get a certain cancer after being infected with these viral bacteria. There is no country in the world that classifies cancer as a contagious disease, and there is no hospital that takes isolation measures for cancer patients. Moreover, you must have observed the phenomenon that oncology doctors do not take isolation protection measures at all when treating cancer patients. Sometimes doctors wear masks during treatment activities only for other medical purposes, not for cancer prevention at all, and not only oncology doctors, but also any professional doctors have to wear masks and hats during certain treatment operations. In addition, in fact, the cancer incidence rate of medical personnel in oncology departments of specialized hospitals or general hospitals is not higher than that of the general population, and because they know more about cancer prevention and treatment, their probability of getting cancer may be lower. The truth is: people living in the same area or the same family are more likely to get cancer or tend to get the same kind of cancer, and cancer seems to be “contagious”, but in fact, the so-called “contagious” cancer is only caused by the same or similar environment, that is, they live in the same or similar cancer-causing environment. In fact, the so-called cancer “contagion” is only caused by the same or similar environment, that is, they live in the same or similar cancer-causing environment, have similar lifestyles in the same area or experience the same environmental pollution; couples have highly similar lifestyles and habits. These poor lifestyles or habits or environmental pollution are important factors that lead to the occurrence of cancer. It is not that cancer is contagious, but that they are exposed to the same or similar cancer-causing environment, thus developing cancer in a relatively concentrated way. Therefore, please bear in mind that if your family members or friends or relatives unfortunately have cancer, please spend more time with them, don’t discriminate, give them more care and attention, don’t prevent and hide, don’t rub salt on their wounds, and don’t bring them double physical and mental harm.