According to the World Health Organization, 1/3 of tumors can be prevented, 1/3 can be cured, and 1/3 can be significantly improved by treatment. There are three levels of cancer prevention, as follows: 1. Primary prevention is prevention from etiology, reducing high-risk factors that cause cancer, for example, common behavioral patterns such as smoking, alcohol abuse and betel nut chewing are clearer cancer-causing factors. Secondly, to avoid physical and chemical exposure to cancer-causing factors, such as exposure to ionizing radiation like X-rays and cancer-causing chemicals, reducing such exposure is called primary prevention in terms of etiology; 2. Secondary prevention advocates early diagnosis, early treatment and early detection, called the three early stages. In the process of prevention, cancer should be screened, detected early, then diagnosed and treated early; 3. Tertiary prevention is to do related treatment after cancer diagnosis to improve patients’ survival and quality of life. It can be accurately said that cancer is preventable and treatable.