Extrapolations are the Achilles Heel of Risk Assessment

This Reflections article considers the problems associated with the various extrapolations that are required for the estimation of human cancer risks from exposure to environmental carcinogens at low doses. These include extrapolation between species (particularly rodent to human), from responses at high doses to those at low doses, and among different stages of life. Reductions in uncertainty in risk estimates are closely coupled to the ability to conduct reliable extrapolations. The best way forward appears to be the use of data on mechanisms of carcinogenesis to develop bioindicators of responses related to the pathway to tumor formation. Such an approach is proposed based on the phenotypes represented by the six acquired characteristics forming the Hanahan-Weinberg model for carcinogenesis (The Hallmarks of Cancer). In addition, approaches can be established that use the Hanahan-Weinberg model as the basis for the collection and/or analysis of microarray or similar data. The reduction in reliance on default options and safety factors in the risk assessment process is a real possibility.