Colorectal cancer happens when cells in your colon or rectum grow abnormally and out of control. It may start in a polyp, or small growth, in your colon or rectum. The cancer cells can spread to other parts of your body.

This cancer is also called colon cancer or rectal cancer, depending on where the cancer is. It is most common in people older than 50.

Treatment works best when the cancer is found early. Screening tests can help find polyps and can find cancer that is still in its early stages and hasn't spread yet.