Cancer epidemiology

The assessment of causal relationships between exposure and disease usually requires epidemiological studies. Randomized trials on humans are rarely achievable but can sometimes be accomplished in a secondary follow-up of the long-term side effects, e. g., of drugs. The association between smoking and lung cancer is a classical example of important information discovered by epidemiological studies. Other important epidemiological achievements include detecting the relationship between asbestos exposure and mesothelioma, arsenic exposure and lung cancer, and vinyl chloride and hemangiosarcoma of the liver. The epidemiological approach has been criticized because of its nonexperimental nature, but there is no other ethically acceptable way to confirm whether toxicologic observations of an adverse health effect are relevant for humans. However, epidemiological studies must be carefully conducted and evaluated since methodologic limitations may influence the studies as well as the interpretation of the findings.