Cancer has been called “the plague of the 21st century”. For a long time, the prejudice that cancer is an incurable disease has led people to the misconception that cancer is mainly determined by genetic factors and the cause of the disease is unclear and cannot be prevented. In fact, cancer, like other diseases, can be prevented. A large number of studies have confirmed that acquired environmental factors acting on the susceptible genes of the body are the key factors leading to the occurrence of cancer. Genetic genes cannot be changed, but acquired factors can be avoided and changed. If prevention is carried out for a certain cancer and some habits with clear cancer-causing factors are changed, the incidence of cancer can be completely reduced. On the occasion of the 16th National Cancer Awareness Week, we would like to remind everyone to take action to prevent cancer from sneaking in. The first line of defense: stay away from the five major cancer-causing factors. At present, there are five main categories of cancer-causing factors: (1) environmental pollution, including pollution of atmosphere, water and soil; (2) cancer-causing factors in personal habits, such as smoking and eating moldy food; (3) natural carcinogens, such as fungi, viruses, plants and sunlight; (4) occupational carcinogens, such as long-term exposure to radiation, rubber and asbestos; (5) endogenous carcinogens, i.e. certain metabolites of human body, such as amines and nitrites in food that enter the stomach; (6) endogenous carcinogens, i.e. the metabolites of human body that enter the stomach. amines and nitrites in food, which are changed into carcinogenic amines nitrite under the action of low acid and bacteria, etc. The 2nd line of defense: correcting poor lifestyle. Cancer is a disease caused by poor lifestyle. Correcting poor lifestyle has the potential to reduce the occurrence of cancer. Bad lifestyles mainly include the following seven aspects: (1) food, such as too much salt can easily cause stomach cancer, high-fat diet can easily cause breast cancer and colon cancer, etc.; (2) smoking, the occurrence of lung cancer, bladder cancer, esophageal cancer, pancreatic cancer, cervical cancer and many other cancers are related to smoking; (3) excessive alcohol consumption. According to statistics, about 3% of all cancers are caused by alcohol consumption. Because alcohol can suppress the immune system, reduce the detoxification function of the liver and increase the absorption of carcinogens in the stomach. (4) Infection, many kinds of cancers are related to bacteria, fungi and viruses; (5) Sexual and reproductive factors, emphasizing healthy sexual life; (6) Sunlight, which can also cause tumors, such as skin cancer; (7) Occupation and environment. The 3rd line of defense: regular medical checkups. The clinical manifestations of cancer are not very specific in many cases, and many patients are already in the middle and late stages when they are discovered, losing the best time for treatment. To enhance the awareness of self-care, regular medical check-ups can help detect cancer at an early stage. For example, if one wakes up in the morning and inhales blood sputum backwards, one should be alerted to nasopharyngeal cancer; if one has stagnant induction in eating, one should be alerted to esophageal cancer; if one has increased frequency of stools, alternating dry and thin stools, or alternating diarrhea and constipation, one should be alerted to colon cancer; if one has painless hematuria, one should be alerted to kidney cancer; if one has vaginal bleeding after menopause or irregular vaginal bleeding before menopause, especially contact bleeding, one should be alerted to cervical cancer. Clinical practice proves that many cancers have a better prognosis if detected early and treated actively and effectively, and some of them can even be cured clinically. The 4th line of defense: actively prevent and treat precancerous lesions. As the saying goes, “three feet of ice is not a day’s cold”. It is a long process for a normal cell to evolve into a cancer cell, which usually takes several decades. This provides us with the opportunity to have enough time to intervene early and interrupt the development of non-normal cells. Examples are precancerous lesions such as oral leukoplakia, cystic hyperplasia of the breast, chronic atrophic gastritis, chronic hepatitis B, familial multiple colon polyps, ulcerative colitis, cervical erosion, and cryptorchidism. These diseases are not cancerous in themselves, but have a very high chance of evolving into cancer. If timely and effective treatment is provided to interrupt their evolution, the incidence of certain cancers will be significantly reduced. In addition, cancer is not an infectious disease, but some cancers are related to infections. For example, stomach cancer is associated with Helicobacter pylori, cervical cancer with human papillomavirus, and liver cancer with hepatitis B or C infection. Early treatment of these infections can also significantly reduce the occurrence of the corresponding tumors. Therefore, people should pay attention to this and prevent cancer before it happens. The 5th line of defense: strengthen physical fitness and keep the body and mind healthy. As mentioned in Chinese medicine, “movement is the outline and vegetation is the norm” and “a broad mind and strong body” are the truths to prolong life and the secrets to prevent and fight against cancer. Modern medicine also believes that the decline of the body’s immune function is an important internal cause for the occurrence of cancer. Therefore, insisting on exercise and keeping a happy mood and strong body will be beneficial to prevent cancer.