Controlling the avoidable causes of cancer: needs and opportunities for etiologic research.

This meeting of the President's Cancer Panel was designed to provide an overview of known and suspect causes of cancer and to indicate those that might be considered avoidable. Two complex concepts are inherent in this charge: cause and avoidability. Risk factors for cancer are designated as causal when the evidence from observational and laboratory research is judged sufficient in relation to criteria for causality; the extent to which cancers of specific sites can be avoided is best estimated by the attributable risk statistic, which incorporates both the exposure pattern and the relative risk for the cancer-causing agent. A research agenda on avoidable causes of cancer should then address both the risks associated with the agents that cause cancer and the pattern of exposure to the agents. Presentations at the meeting highlighted gaps in the evidence on the risks associated with various known and potential causes of cancer and on the patterns of exposure across the diverse groups within the population. In spite of these gaps, presenters emphasized that the evidence is already sufficient to justify intervention for many agents and that action need not be delayed for the well-characterized causes of cancer. In addition to research recommendations offered by presenters for specific causal agents, the scientific basis for cancer prevention might be generally strengthened by new research strategies directed at developing new tools for exposure assessment, for investigating the risks of mixtures, and for population surveillance.