For most of the tumors, the exact etiology is still unclear and is divided into two categories, exogenous and endogenous, based on the differences in their origin, nature and mode of action. 1. Exogenous factors: (1) Chemical factors: according to their mode of action, they are categorized into direct carcinogens, indirect carcinogens and carcinogens. Common chemical carcinogens include polycyclic aromatic hydrocarbons, aromatic amines and azo dyes and nitrosamines. (2) Physical factors: Ionizing radiation is the most important physical carcinogen. (3) Biological factors: mainly viral infections, such as hepatitis B virus and primary liver cancer, EB virus and lymphoma and nasopharyngeal carcinoma, human papilloma virus and cervical cancer and oral cancer. 2. Endogenous factors: (1) Gene mutation: tumor diseases are often associated with mutation of certain proto-oncogenes and oncogenes. (2) Endocrine factors: such as estrogen and prolactin are related to breast cancer, estrogen is related to endometrial cancer, and androgen is related to prostate cancer. (3) Immune factors: congenital or acquired immunodeficiencies are prone to malignant tumors, such as leukemia and lymphohematopoietic system tumors in patients with gammaglobulin deficiency, and malignant tumors in patients with acquired immunodeficiency syndrome (AIDS). It is recommended that people with the above high-risk factors undergo regular medical checkups for early detection of diseases and early treatment to avoid delays.