Prevention is very important. According to the concept of preventive medicine, the prevention of cancer is divided into three levels: First level prevention: it is to reduce or eliminate the carcinogenic effect of various carcinogenic factors on human body and reduce the incidence rate. It can be understood as the active prevention of disease from the perspective of disease occurrence, also known as etiological prevention. We can take the following measures: 1. take care of physical exercise and weight control; 2. work and rest reasonably to maintain vigorous energy so as to improve immune function and disease resistance; 3. get out of depression as soon as possible; 4. pay attention to diet and water hygiene to prevent cancer from entering by mouth; do not eat moldy, rotten or burnt food, as well as smoked, baked, pickled or soaked food, and do not drink water that has been stored for a long time; 5. 5.No smoking, no alcoholism, scientific diet, more fresh vegetables, fruits and nutritious foods, and good hygiene habits; 6.At the same time, ensure the air quality of small environment (working environment, second-hand smoke, oil smoke, etc.) and large environment (living environment), avoid or reduce air pollution as much as possible, which can prevent physical, chemical, parasitic and viral carcinogenic factors from attacking human body and prevent cancer from the first step. prevent the occurrence of cancer. Second level prevention: It is to reduce the death of cancer patients by using effective means of early detection, early diagnosis and early treatment. It can be understood that even if a tumor appears, it should be detected and treated as early as possible. How to detect tumor as early as possible is a problem that the whole society is concerned about. The common methods are: 1.Health education: With basic health knowledge, you can self-manage your health, and you can also detect abnormalities at the first time. 2, regular routine physical examination: such as blood routine, urine routine, stool routine, if abnormal or can reflect a lot of problems earlier. 3.Targeted physical examination for high-risk groups: such as low-dose high-resolution CT and bronchoscopy can detect early lung cancer; B-ultrasound and methotrexate can detect liver cancer; routine vaginal cytology examination can detect cervical cancer at an early stage; esophageal screening and fiber esophagoscopy can detect esophageal cancer at an early stage. And we often emphasize gastroscopy and colonoscopy for stomach cancer and colorectal cancer respectively. 4.After cancer is found, it is better to go to a specialized oncology hospital for diagnosis and treatment, establish confidence in overcoming cancer and actively cooperate with treatment, many cancers can be cured, especially in early stage. Tertiary prevention, clinical prevention and rehabilitative prevention: the goal is to prevent the deterioration of the disease, prevent disability, adopt multidisciplinary comprehensive diagnosis and treatment, correctly select reasonable treatment plan, provide radical treatment for patients who can be cured, so as to achieve the purpose of cure; provide palliative treatment and terminal treatment for patients who can no longer be cured, so as to eliminate pain, restore physical strength, prolong survival time and improve the quality of life; in treating cancer, we seek to prevent cancer recurrence and metastasis, and prevent complications and sequelae. This point can be understood as: standardized, rational and individualized treatment. All oncology specialty hospitals have the advantages of comprehensive treatment, and have different treatment methods for different tumor diseases, including surgery to remove tumor, chemotherapy, radiotherapy, immunotherapy, targeted therapy and comprehensive treatment.