Cancer is a leading cause of death in human. Main risk factors of cancer includes:
1. Host genetic factors.
2. Lifestyle or environmental factors, such as food, physical activities, smoking, alcohol, aflatoxin, arsenic, asbestos, ultraviolet, and ionizing radiation, etc.
3. Infection : such as carcinogenic virus, bacteria, or parasite infection.

While the incidence of cancer is much higher in adults, the action of cancer prevention can be started from childhood. Besides screening of the genetic factors to find out the high risk groups for specific cancers, establishment of healthy life styles starting from childhood to prevent obesity, exposure to environmental carcinogens such as smoking, alcohol, radiation,etc. are also very important.

Among the infectious agents with carcinogenic evidences, successful vaccines have been developed for hepatitis B virus (HBV) and human papilloma virus (HPV). Vaccines are still developing for other viruses (such as, hepatitis C virus, EB virus, human immunodeficiency virus), and bacteria ( H. pylori).

Immunization against carcinogenic biologic agents is a cost effective way to prevent cancer. HBV vaccine is the first human cancer preventive vaccine with high efficacy. Liver cancer is one of the five leading causes of cancer death globally. Due to mother-to-infant transmission as the main route of chronic HBV infection and liver cancer, immunization since birth is the best timing to prevent liver cancer. We have provided evidences to support the success of reduction of chronic HBV infection and liver cancer in children. Recently, we have also proved that the cancer preventive effecto fo HBV immunization has been extended from children to adolescents of 6 to 19 years old. This experience could be shared with other cancer preventive vaccines, such as HPV vaccine to prevent cervical cancer, in the future.

In conclusion, cancer preventive works should be started from early childhood.