Anyone can get colorectal cancer, and doctors don't always know why someone gets it.
Although scientists don’t know the exact cause, they do know some of the things that make people more likely to get it. These include:
Age. The disease is most common in people over age 50, and the chance of getting colorectal cancer increases with each decade. But younger people can get it, too.
Polyps. These growths on the inner wall of the colon or rectum aren’t cancer. They’re fairly common in people over age 50. One type of polyp, called an adenoma, makes colorectal cancer more likely. Adenomas are the first step toward colon and rectal cancer.
Personal history. If you’ve already had colorectal cancer, you could get it again, especially if you had it for the first time before age 60. Also, people who have chronic inflammatory conditions of the colon, such as ulcerative colitis or Crohn's disease, are more likely to develop colorectal cancer than other people.
Family history. Do you have a parent, brother, sister, or child who has had colorectal cancer? That makes you more likely to get it, too. If two or more close family members have had colorectal cancer, then you have about a 15% chance of getting it at some point. If conditions such as familial adenomatous polyposis, MYH-associated polyposis, or hereditary nonpolyposis colon cancer run in your family, that raises the risk for colon cancer (and other cancers), too.
Race. African-Americans are more likely than other U.S. racial and ethnic groups to get colorectal cancer. Doctors don’t know why that is.
If you have one or more of these risk factors, it doesn’t mean that you will develop colorectal cancer. But you should talk about your risk factors with your doctor. She may be able to suggest ways to lower your chances and tell you when you need to get checked.