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Cancer and other diseases can be triggered by exposure to toxic agents. The presence and concentrations of such agents may vary geographically. Toxic agents that can increase cancer risk include:

  • Chemicals in the air, water, and/or food supply, such as asbestos (air) and arsenic (water).
  • Radiation. This includes both naturally occurring ultraviolet (UV) radiation from the sun and man-made radiation from nuclear accidents.
  • Bacteria and viruses, such as H. pylori, human papillomavirus (HPV), hepatitis, and HIV.

Because many cancers develop over a long period of time, knowing the spatial context throughout a person's life is important to understand his or her total exposure to toxic agents. Recently, scientists have discovered that some cancers are caused by a combination of an underlying genetic abnormality coupled with environmental exposure. Such "gene-environment" interactions further emphasize the importance of spatial context.

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