How the initial cancer cells are formed is a question that has always troubled mankind, or rather, what is the cause of cancer? The development of cancer goes through a complex process. Genetics is involved, as well as a variety of carcinogenic factors in the environment. In the case of genetic issues, it has been known for a long time that there are so-called cancer families. In the family history, certain cancers have occurred in multiple generations. Patients with certain hereditary diseases are also prone to cancer, and some scholars believe that it takes more than 2 mutations for normal cells to evolve into cancer cells. Such mutations, or chromosomal rearrangements, involve proto-oncogenes as well as oncogenes. These genetic changes, which control cell differentiation, proliferation, etc., lead to cellular carcinogenesis. In people with a family history of cancer, there may already be some kind of “inheritance”. The combination of pre-existing disorders with environmental carcinogens makes it easier to induce cancer. Some experiments have also confirmed that people with “genetic disorders” may be more susceptible to stimulation by carcinogenic factors. The research on carcinogenic factors has been very advanced. Nowadays, there are chemical, viral and physical factors. Chemical carcinogenic factors were first studied from coal tar. Modern known chemical carcinogens have a wide range. Familiar ones such as alkylating agents, benzo(a)pyrene, nitrosamines, certain heavy metals and other mycotoxins that often lead to food contamination, thermal cracking products of food, cigarettes and other hobby products. Carcinogenic factors cause cancer and are generally considered to go through three stages. That is, initiation, promotion and evolution or evolution. Some carcinogenic agents may act in the initiation stage and some may act only in the promotion stage. Viral factor carcinogenesis is a hot topic in basic tumor research. reverse transcriptase, which was discovered in the 70s, is of great value for in-depth study. The papillomaviruses of modern RNA viruses are known to be associated with cervical cancer in humans; herpes simplex virus is also associated with cervical cancer; EBV is associated with certain lymphomas and nasopharyngeal cancer; hepatitis B and C viruses are associated with liver cancer; and T-cell leukemia virus of RNA viruses is associated with certain leukemias; the virus of AIDS, too, is associated with cancer in humans. Physical factors can also cause cancer, such as radiation from atomic bomb explosions. These exogenous carcinogenic factors, interacting with genetic and physical factors, lead to a series of changes that cause carcinogenesis. Besides physical, chemical, biological, and genetic factors, there are also endocrine, mental, immune, and some other factors that are closely related to the occurrence of tumors.