Age over 50 Colorectal cancer is more likely to occur as people get older. More than 90% of people with this disease are diagnosed after age 50. The average age at diagnosis is 72.
Colorectal polyps Polyps are growths on the inner wall of the colon or rectum. They are more common in people over age 50. Most polyps are benign (not cancerous), but some polyps (adenomas) can become cancer. Finding and removing polyps may reduce the risk of colorectal cancer.
Family history of colorectal cancer Individuals whose close relatives (parents, brothers, sisters, or children) have a history of colorectal cancer are somewhat more likely to develop this disease themselves, especially if the relative developed the cancer at a young age.
Genetic alterations

Changes in certain genes increase the risk of colorectal cancer:

  • Hereditary nonpolyposis colon cancer (HNPCC) is the most common type of inherited (genetic) colorectal cancer. It accounts for about 2 percent of all colorectal cancer cases. It is caused by changes in an HNPCC gene. Most people with an altered HNPCC gene do develop colon cancer, so genetic testing may be appropriate.
  • Familial adenomatous polyposis (FAP) is a rare, inherited condition in which hundreds of polyps form in the colon and rectum. It is caused by a change in a specific gene called APC. Unless FAP is treated, it usually leads to colorectal cancer by age 40. FAP accounts for less than 1 percent of all colorectal cancer cases.
Personal history of cancer A person who has already had colorectal cancer may develop colorectal cancer a second time. Also, women with a history of cancer of the ovary, uterus (endometrium), or breast are at a somewhat higher risk of developing colorectal cancer.
Ulcerative colitis or Crohn's disease A person who has had a condition that causes inflammation of the colon (such as ulcerative colitis or Crohn's disease) for many years is at increased risk of developing colorectal cancer.
Unhealthy Diet Studies suggest that diets high in fat (especially animal fat) and low in calcium, folate, and fiber may increase the risk of colorectal cancer.
Cigarette smoking A person who smokes cigarettes may be at increased risk of developing polyps and colorectal cancer.