The causes of tumor formation are as follows: First, it is mainly caused by genetic mutations, such as the formation of oncogenes, which are nucleic acid fragments that can transform normal cells into tumor cells, and are firstly found in RNA viruses. Second, tumor suppressor genes are significantly reduced, and their loss or loss of function can lead to cell deterioration. Thirdly, apoptosis regulation genes, the growth of tumor depends on the ratio of cell proliferation to apoptosis, if this balance is broken, it will easily cause tumor. Fourth, poor function of DNA repair genes causes tumor formation. The common chemical, physical and biological carcinogenic factors are as follows: First, chemical carcinogenic factors, such as carcinogenic aromatic amines, amines nitrites, fungal toxins, such as Aspergillus flavus, etc. Second, physical carcinogenic factors, such as ultraviolet light and ionizing radiation. Third, biological carcinogenic factors, such as Schistosoma chinensis, chronic schistosomiasis, human papilloma virus, as well as hepatitis B virus, hepatitis C virus, Helicobacter pylori, etc.