While many risk factors for cancer have been identified, it is often difficult to study the effects of many suspected carcinogens, particularly when low levels of exposure are involved. International projects that are implemented in several centres can study the relatively large populations needed to investigate small risks. Markers of genetic susceptibility allow the identification of individuals that are at particularly high risk and to elucidate the carcinogenicity of exogenous agents. In addition, the use of biomarkers of dose and of early effects has the potential to yield better assessments of exposure and outcome.
