The incidence of malignant tumors has been on a significant rise in recent years. You will encounter more and more cancer patients in your life and work. “Is cancer contagious?” This is a question that many people directly face and are extremely concerned about. Does cancer mean death? Is it better to be as far away from cancer patients as possible? Many people have misconceptions about this issue, and this has caused serious psychological damage to cancer patients. A female patient was openly optimistic and actively cooperated with doctors after discovering liver cancer. When a friend had a new grandson, she and another old classmate who had bowel cancer gladly went to visit. After having tea and talking, the classmate with bowel cancer had to leave beforehand, and the host immediately threw her used teacup into the garbage, saying that cancer patients used it, it is not good! She wanted to hug the child, and the host’s fearful expression overwhelmed her. The lady left in dismay and never dared to go to any friend’s house again. A young worker with lung cancer was told by the doctor that the operation was successful, that no other treatment was necessary for early stage lung cancer, and that he could act like a normal person in the future. He was very happy. However, after he went to work, he was alone, as his friends avoided him, and he was no longer able to eat and laugh together. Some even threatened to transfer him to avoid infecting others. He has been home sick since then, without any social activities. “Is cancer contagious?” We often see that in the same family, there are multiple family members with cancer, and even unrelated family members (such as husband and wife) both have cancer, and sometimes the same kind of cancer. In addition, cancer can occur one after another among workers in a certain unit, such as workers in a chemical plant. Does this prove that “cancer is contagious”? Oncologists clearly point out that cancer is not contagious, so please show more warmth and care to cancer patients. Cancer is essentially the unrestricted growth of cells in the body, which leads to the extrusion, invasion and destruction of normal tissues. The causes of cancer include four types: heredity, certain viruses, chemical carcinogens and ionizing radiation. However, the above four etiologies only increase the chance of developing cancer, they do not cause cancer to occur 100%. In other words, there is no real causative agent of cancer. For example, smoking increases the incidence of lung cancer, but smokers do not get lung cancer 100% of the time. Another example is that a higher percentage of hepatitis B virus carriers develop liver cancer, but not all hepatitis B hepatitis patients eventually become liver cancer patients. A lot of research shows that the occurrence of cancer is a multifactorial, multi-stage, complex and gradual process, which includes not only external factors, but also genetic factors, immune status and other individual factors. Some families have multiple cancer cases, which may be related to the fact that some cancers are hereditary in families, and the oncogenes are passed within blood relatives, leading to multiple cases. For example, if a mother or sister is a breast cancer patient, she is three times more likely to develop breast cancer than the average woman. Patients with colorectal and ovarian cancers are also significantly more likely to have cancer in their immediate family than in the general population. But how to explain that unrelated family members (such as husband and wife, son-in-law, etc.) have the same type of cancer? One scenario is that they share the same dietary habits or are exposed to the same cancer-causing factors. In one such case, both husband and wife died of liver cancer. The medical history revealed that they both suffered from hepatitis B for many years. As we all know, hepatitis B is caused by the hepatitis B virus, which can be transmitted through blood or other body fluids, including saliva, semen and vaginal secretions. Hepatitis B can cause cirrhosis if left untreated for a long time, and a few patients will eventually develop liver cancer. There is also a report that both father-in-law and son-in-law suffered from lung cancer. After investigation, it was learned that the son-in-law had taken over the job of his father-in-law and was engaged in underground work in a mine where the concentration of radon was too high. Since they were exposed to such radioactive substances for a long time, it caused lung cancer. In addition, both husband and son-in-law were smokers, which undoubtedly added to the problem and contributed to the formation of tumor. Epidemiologically speaking, cancer is not an infectious disease either. Infection, in common terms, is the spread of a disease from one person to another by some means. There are three necessary conditions for contagion: source of infection, transmission route and susceptible people, none of which is necessary. If cancer is really contagious, there should be pathogens such as SARS virus, Mycobacterium tuberculosis and Bacillus anthracis. In fact, there is no real pathogen that causes cancer, so cancer patients are not the source of infection and cancer is not contagious. The following facts prove that cancer is not contagious. For example, when a surgeon performs surgery on a cancer patient, sometimes the glove breaks and blood or tissue debris from the cancer patient can get on the surgeon’s finger through the broken glove. If cancer were contagious, surgeons would have had at least hundreds of infections during their long hours of surgery, and would have developed cancer long ago, but in fact surgeons have the same cancer rate as the general population. Doctors, nurses and caregivers who are in close contact with cancer patients in the hospital are not known to have been infected with cancer. The survey shows that the incidence of cancer among medical staff and researchers who are engaged in cancer prevention and treatment is not higher than that of the general population in the same area. In addition, couples who live together for a long time and one of them has cancer, the spouses do not infect each other. Animal studies have also shown that cancer is not contagious: healthy mice were kept with cancer-stricken mice for a long time without any signs of cancer in the healthy mice. Can closer contact, such as inoculating cancer cells from a patient directly on a normal human body, give rise to cancer? The answer is clear, no. In other words, although cancer cells can spread and metastasize in a patient’s body, unlike bacteria and viruses, it is not transmitted from one person to another. Surgeons or operating room nurses sometimes accidentally injure their own skin during cancer surgery, which is similar to a direct inoculation of cancer cells, but there have been no reports of health care workers getting cancer as a result. There have been studies in which live cancer cells were inoculated in “volunteers” in an unsuccessful attempt to obtain specimens of the same cancerous tumors. To oneself, another person’s cancer cells are a foreign substance that the body’s immune system destroys and kills through strong immune rejection, so it is impossible to inoculate tumor cells successfully. Other people’s cancer cells cannot come to their own body to survive. Therefore, the fear of cancer cell inoculation infection, or the concern of direct contact infection when in close contact with cancer patients are unnecessary. Changing bad habits and maintaining a healthy lifestyle are the most effective measures to prevent cancer at present (for details, please refer to the WHO 15 key rules for cancer prevention). Therefore, we call for the strengthening of cancer popularization, the fact that cancer is not contagious, and the dedication of warmth and care to cancer patients.