Because a number of mutations usually must occur for cancer to arise, the chances of developing cancer increase as a person gets older because more time has been available for mutations to accumulate. For example, a 75-year-old person is a hundred times more likely to develop colon cancer than a 25-year-old. Because people are living longer today than they did 50 or 100 years ago, they have a longer exposure time to factors that may promote gene changes linked to cancer.
![Cancer Risk and Aging](https://webarchive.library.unt.edu/eot2008/20090510045857im_/http://www.cancer.gov/images/Documents/4167b7ca-7e27-4eec-9855-640637dde5dc/cancer38.jpg)
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