Ca is the abbreviation of Cancer in English, which is translated as cancer in Chinese. Cancer is a malignant tumor originating from epithelial tissue, and its occurrence is related to the following factors: 1. bad living habits, such as smoking, drinking strong alcohol, eating too hot food, unreasonable diet, such as high-fat diet, often eating moldy food, etc. 2. environmental pollution, pollution of air, drinking water and food can cause harm to human beings, and the carcinogenic substances that have been announced by the World Health Organization include arsenic, asbestos, benzidine, 3.Infection, mainly viral infection, such as hepatitis B virus and aflatoxin are related to the occurrence of liver cancer; human papillomavirus infection is related to cervical cancer; Helicobacter pylori infection is related to the occurrence of gastric cancer; EBV infection is related to the occurrence of nasopharyngeal cancer. 4.Radiation, such as radionuclides, X-rays, ionizing radiation, etc. 5.Endogenous factors including genetic factors, immune factors, such as congenital or acquired immunodeficiency diseases are prone to tumors. 6, endocrine factors, such as estrogen and prolactin are related to the occurrence of breast cancer. It is recommended to do the tertiary prevention of tumor to reduce the occurrence of tumor.