The environment influences cancer rates and risks. We can see this by comparing cancer rates in different countries, and how rates change when people move from one country to another.

For example, U.S.-born Japanese men have twice the rate of colon cancer as native-born Japanese men, and U.S.-born Japanese women have colon cancer rates 40 percent higher than their counterparts born in Japan. So scientists study what exposures or characteristics differ between Japanese immigrants and their descendants in the U.S. to better understand the environmental factors that may be influencing their colon cancer rates and risks.