The etiology of cancer is not yet fully understood. The following factors are more clearly understood: 1. Bad living habits: such as smoking, intake of large amount of strong alcohol, high energy and high fat diet, pollution of drinking water, moldy food, etc.; 2. Chemical or physical carcinogens in the environment enter the body through the body surface, respiratory tract and digestive tract to induce cancer; 3. Biological factors: under certain conditions, they can also cause cancer. Biological factors are usually carcinogenic by viruses; 4. Trauma and local chronic inflammatory stimulation: burns, scars and chronic skin ulcers can also be carcinogenic; 5. Some medical examinations and treatments also have carcinogenic possibilities; 6. Direct genetic tumors are only a minority, and most genetic factors only increase the body’s propensity to tumors and susceptibility to carcinogenic factors; 7. Congenital and acquired immune defects, which are also prone to malignant tumors; 8. Hormonal abnormalities in the body are also one of the factors that induce cancer.