His major interest is in cancer epidemiology, risk factor analysis, genetic susceptibility and preventive measures. In 1992, he conducted a multi-center collaborative study to establish a community-based prospective cohort (KMCC), that is the first genomic cohort in Korea and one of the distinguished cohorts with biologic specimen bank in the world. He has continued to contribute to the newly constructed Korean genome cohort studies as the PI. He has served as the president of the Korean Genome Epidemiology Society since 2005. He led the Asian Cohort Consortium to establish a cohort of at least one million healthy people through partnership with other cohorts since 2005. As the Secretary General of the Asian Pacific Organization for Cancer Prevention since 2006, he is devoted to enhance cancer control strategies in developing countries through transfer knowledge, capacity building, and exchanging cancer control activities in the region. He was the President of the National Cancer Center of Korea from 2006-2008, and led the National Cancer Control Program in Korea.