Molecular epidemiology: a tool for understanding mechanisms of disease.

The use of biomarkers in medicine, and in epidemiology in particular, is not new but recent developments in molecular biology and genetics have increased the opportunities for their use. Epidemiological studies based on biomarkers, which belong to the discipline defined as 'molecular epidemiology', offer new avenues to investigate associations between genetic and environmental factors, diseases, and medical interventions. Important recent contributions of molecular epidemiology to cancer research include the definitive evidence of the carcinogenicity of aflatoxin in humans, and the elucidation of the mechanisms of tobacco-related carcinogenesis. However, molecular epidemiology studies are subject to problems of design and analysis similar to those of 'traditional' epidemiological studies. If biomarkers offer new opportunities to overcome some of the limitations of epidemiology, their added value over traditional approaches should be systematically assessed. Biomarkers should be validated though transitional studies; consideration to sources of bias and confounding in molecular epidemiology studies should be no less stringent than in traditional studies.