Cancer occurs throughout the world, but the risk of cancer varies from region to region, suggesting geographic, environmental, and cultural implications.
Cancer incidence is monitored by population-based tumor registries around the world.
Not all countries maintain population-based tumor registries and in many countries, including the United States, these registries monitor considerably less than the entire population. To make meaningful comparisons among different countries, the rates are age-adjusted to the world standard population. The effect of age-adjustment is to eliminate differences in rates when the population of one country has a different age distribution from that of another country. Many countries have vital statistics departments which keep track of cancer deaths for the entire country, providing a broad base for comparing cancer mortality rates across countries. For many specific cancers, and for all cancers combined, there are wide variations in death rates among different countries.