Since the 20th century, studies on epidemiology, high incidence areas and occupational cancers have provided a lot of reliable clues and bases for finding and determining the causes of tumors. Some of the more important ones are: 1. Smoking There have been many studies on the etiology of lung cancer. The relationship between smoking and lung cancer has been proved by a large number of facts. Smoking is a recognized cause of lung cancer, but the proportion of smokers suffering from lung cancer is less than 20%. Smoking is associated with not only lung cancer but also cancers of the mouth, hypopharynx, esophagus, stomach, bladder, and cardiovascular disease. Worryingly, according to a recent survey, the proportion of smoking among urban high school students in China is 30%-40%. 2. Radiation and ultraviolet light Exposure to ionizing radiation from nature or industrial, medical and other sources can cause a variety of cancers, including leukemia, breast and thyroid cancers. Bone, hematopoietic system and lung are organs sensitive to radiation. Japanese atomic bomb victims developed leukemia in the acute phase; thyroid or lung cancer rates were increased among atomic bomb victims in the chronic phase and among patients who had previously been irradiated for arthritis in the spine. Sunlight is a major source of ultraviolet radiation, and long-term UV exposure can cause skin cancer, especially in highly exposed Caucasian populations. Very low frequency electromagnetic fields may also be related to cancer, but it is not conclusive. 3.Chemical carcinogens Many compounds are carcinogenic. For example, benzo(a)pyrene contained in cigarettes has strong carcinogenic effect and can cause skin cancer and lung cancer. Aflatoxin produced by aflatoxin contaminated food may cause liver cancer. Arsenic can cause skin cancer, lung cancer and liver cancer. Currently recognized chemical carcinogens are also asbestos, chromium, nickel, coal tar, mustard gas, mineral oil, dichloromethyl ether, and so on. The most important chemical carcinogens for the total human cancer risk are currently considered to be the many carcinogenic components of cigarettes. Other chemical carcinogens are mainly combustion and organic synthesis products, certain food components, microbial contamination products, or substances resulting from food preparation processes. In addition, certain physiological and pathological processes in the human body itself, such as inflammation, oxidative stress, nutritional and hormonal imbalances, and repeated tissue damage, can also produce carcinogenic chemicals such as oxygen radicals. It is estimated that among human cancers caused by environmental factors, chemical carcinogenic factors occupy a major position. Although most tumors are not transmissible, it is clear that certain RNA viruses such as human T-cell leukemia virus-1 (HTLV-1) and HTLV-2 viruses can cause leukemia and lymphoma; certain DNA viruses such as hepatitis B virus (HBV) and hepatitis C virus (HCV), EBV, and high-risk human papillomavirus (HPV) can cause liver cancer, hepatitis B and hepatitis C cancer, respectively. can cause hepatocellular carcinoma, Burkitt’s lymphoma, nasopharyngeal carcinoma, Hodgkin’s lymphoma, and cervical cancer, respectively. More recent data also suggest that Helicobacter pylori (H, pylori, Hp) is also carcinogenic and is associated with the development of gastric lymphoma. At least eight viruses have now been shown to be associated with a number of tumors in humans, although the degree of certainty of their relevance varies. Other biologic factors that cause cancer include some bacteria and parasites. According to the 1995 data, it is estimated that biological factors cause 18% of all human tumors. 5. Chronic diseases Quite a lot of information illustrates the susceptibility to cancer on the basis of chronic scarring. For example, chronic inflammation of gastric mucosa caused by Helicobacter pylori infection is the basis for the occurrence of gastric cancer. Chronic ulcers of the skin that do not heal for a long time may become cancerous. In northwest China, skin cancer caused by hot bed burn scar is often called “kang cancer”, and there are many colorectal cancers in areas with high incidence of schistosomiasis, which may also be the result of chronic infection. 6.Nutritional factors Nutrition and cancer are also closely related. It is estimated that 1/3 of all human cancers are caused by nutritional factors. It is undoubtedly necessary and beneficial to further determine the role of these factors in the long and complex occurrence of human cancer. Vitamin A and its analogues (commonly known as vincristines) are associated with epithelial differentiation. In the absence of vincristine in food, the sensitivity of experimental animals to carcinogens is increased. The epithelial tissues of the skin, uterus, stomach, trachea, and bronchi of experimental animals were protected against chemical carcinogenesis if supplemented with natural vincristine. Vimentin can inhibit the cell transformation process of normal cells caused by radiation, chemical carcinogens or viruses, and can inhibit migratory cell carcinoma and squamous cell carcinoma induced by chemical carcinogens in rats. In tissue culture, the addition of vincristine can cause the disappearance of squamous metaplasia of epithelium and inhibit the growth of certain tumor cells. Further studies have shown that vincristine can act as an antioxidant to directly inhibit the carcinogenic effect of some carcinogens and inhibit the binding of some carcinogens to DNA, and antagonize the effect of carcinogenic substances, thus directly interfering with the carcinogenic process. In addition, vincristine is essential to control the normal differentiation and growth of many epithelial tissues, has a regulatory role in gene expression, and has a role in the body’s immune system. 7. Immunosuppression The incidence of cancer in patients with organ transplantation requiring long-term application of immunosuppression is significantly higher than that of the general population. AIDS patients are prone to multiple angiosarcomas (Kaposi’s sarcoma) and lymphomas. Various diseases requiring long-term application of immunosuppression should be carefully weighed against the possible hazards. Genetic factors Most human tumors are caused by environmental factors. However, with the same exposure to specific carcinogens, some people develop them while others do not; in addition, some tumors have significant familial aggregation. These facts suggest that the occurrence of tumors is also related to the genetic factors of individuals. It is currently believed that environmental factors are the initiating factors for tumorigenesis, while individual genetic characteristics determine tumor susceptibility. The hottest and most encouraging topic of cancer research in medicine and other biological sciences is currently genetic research. Genetic abnormalities associated with carcinogenesis include mutations or loss of oncogenes, or activation of oncogenes. The causes of these mutations are complex and include viral oncogene insertion, chemical and physical factors that cause mutations and structural damage to genes. Some of these alterations can be inherited, making carriers susceptible to cancer.