Section of Environment and Radiation
Some agents within this scope of environmental, lifestyle, occupational and radiation-related exposures have already been identified as major causes of cancer, particularly tobacco smoking and exposure to ultraviolet radiation, but further characterization of their associated risks is still needed. Ionizing radiation, for example, is a well known carcinogen although the impact of low dose radiation on the overall cancer burden is difficult to quantify.
When it comes to environmental pollutants and occupational exposures, the attributable fraction of the totality of the cancer burden is also difficult to estimate, but is supposedly smaller than from the above-mentioned lifestyle factors or certain infections. Nevertheless, environmental or occupational risk factors are often modifiable by reduction or elimination of exposure, for instance through recommendations to avoid exposure, safety technology or banning of chemicals. If the agents have been scientifically established as risk factors and the political will for action exists, they may represent a greater proportion of the realistically modifiable cancer burden. For some cancers with few known risk factors, the contribution from environmental factors might be larger than currently estimated; candidates include testicular cancer and oesophageal cancer, suggested by the descriptive epidemiology of geographical variation and/or from migrant studies. Also breast cancer, brain tumours or cancers in childhood may have a significant contribution from the environment.
A possible reason for underestimating the impact of environmental and occupational factors is dilution of associations by shortcomings in the characterization of exposure. Additionally, challenges arise in designing studies with sufficient heterogeneity in exposure distributions for ubiquitous environmental exposures, whilst at the same time contrasting comparable population groups in terms of other potential confounding factors. However, exposure assessment in occupational epidemiology has recently improved with the conversion of measurements at work places into more general exposure metrics applicable in large scale epidemiological studies; such improvement is also necessary for environmental exposures and advancement is expected for future studies with the use of biomarkers, exposure modeling and accessibility of secondary data sources.