Speaker – Otto G. Raabe, University of California, Davis Description: Excessive exposure to ionizing radiation may lead to the development of cancer by promotion of ongoing carcinogenic biological processes or by independent cancer induction. Radiation induced cancer is a complex and not completely understood process involving multiple events. The current understanding of radiation carcinogenesis is informed by epidemiological studies of human populations exposed to elevated levels of ionizing radiation and controlled studies utilizing laboratory animals. This review of the major studies provides perspective and suggestions for understanding these seemingly diverse cancer risk phenomena. The conclusions have important implications with respect to ionizing radiation safety standards.