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There is a tremendous geographical diversity in the risk of different cancers. Evidence
from studies of cancer in migrants, who move from one place of residence to another,
confirms that these differences are largely environmental in origin not due to
ethnic or genetic differences and, especially, a product of different lifestyles.
The pattern of liver cancer reflects the prevalence of infection by hepatitis viruses,
especially HBV. One of the main causes of stomach cancer is the bacterium Helicobacter
pylori. Breast cancer is a disease of affluent countries, but it is not rare anywhere,
whereas cervix cancer is largely a disease of the poor south. There are high rates
of cancer of the esophagus in East Africa and Asia, including China and Central
Asia, but testis cancer is rare in African and Asian men.
This sort of information shows the priority areas for research, and indicates where
implementation of current technology would be most fruitful. The global disparities
in incidence of certain preventable cancers (for example, liver and cervix) as well
as in survival from several that are treatable (for example, lymphoma, leukaemia,
and testis) demonstrate a global lack of equity in health care. This is apparently
determined largely by where one lives.
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