Protecting public health in the face of uncertain risks: the example of diesel exhaust

Study design, size, and adequate exposure data as the crucial aspects in cancer risk assessment and implementation of the precautionary principle

Traditional approaches and study design in cancer epidemiology have not been very successful in identifying and evaluating adequately the potential risk and/or protective factors associated with the disease. The main reasons for the failure are often due the small study sample size, and inadequate exposure information. In this paper, issues and approaches relevant to these two challenges are discussed. Multicentre study is proposed as a way to increase study size and to mitigate criticism about meta-analysis of independent studies. A multicentre study of large cohort or case-control studies also offer an exciting opportunity to study the contribution of epigenetic events that may be associated with lifestyle and environmental risk factors for human health. Optimizing methods for exposure assessment and how to reduce exposure to misclassification represent a difficult component in epidemiological studies. A potentially useful approach for improving exposure estimation is to rely on biomarkers of exposures. An example is provided to demonstrate how biomarkers of exposures could provide valuable information in addition to exposure measurements in traditional epidemiological studies. Finally, it is argued that risk assessment and the precautionary principle should not be viewed as conflicting paradigms but, rather, as a complementary approach for developing appropriate policies to address risks posed by exposure to carcinogens and a wide spectrum of other health hazards.

Epidemiological data and cancer risk assessment: cessation LAG and lingering effect concepts

Cessation lag and lingering effect are two important aspects of risk assessment, and have potential applications to dose-response analysis in risk assessment. In addition to providing insight into biological mode of action, the concept of cessation lag is useful for economic benefit analy- sis. Concept of effect lingering can be used to analyze epidemiological data by uncovering the hidden biological implications related to disease endpoints, thereby advancing current efforts to characterize and reduce risk assessment uncertainties. Multicentre study design is proposed as a way to increase study size and to mitigate criticism of meta-analysis of independent studies. Individual studies from a multicentre study can be either pooled using original data, or combined by meta-analysis of summarized results. A multicentre study of large cohort or case-control study also offers an exciting opportunity to study the contribution of epigenetic events that may be associated with life-style and environmental risk factors for human health. Methods for optimizing exposure assessment and reducing exposure misclassification represent important but difficult components in epidemiological studies. Biomarkers present a potentially useful approach for improving exposure estimates.

The identification of human carcinogens and primary prevention of cancer

Primary prevention is based on the incontrovertible logic that a most efficient way to decrease the risk for a disease is to avoid, or reduce to minimal attainable levels, exposures to agents that can cause the disease or contribute to an increase in risk for the disease. This notwithstanding, the adoption of primary prevention measures has often encountered serious obstacles and unjustifiable delays. The success of primary prevention has also been limited by the combined effect of: (a) the inefficient and/or incomplete use of the cumulated etiological knowledge: (b) the spectrum of target organs for human carcinogens which does not include some of the most common cancer sites, a limitation that may be related to a disregard of epidemiological results and case reports that provide evidence that is less than sufficient of a causal relationship between an exposure and human cancer: (c) the pressure that powerful economic interests may have exerted in a variegated way to interfere or delay implementation of preventive measures that could have decreased their profit, and (d) the decreased acceptance of the ability of experimental results to predict similar effects in humans, in spite of the evidence that positive carcinogenicity results in experimental animals have often preceded and could indeed have predicted similar results in humans.