Like most types of cancer, rectal cancer is most common in older people. Over 80% of rectal cancers are diagnosed in people over 60.

The exact cause of rectal cancer is unknown, though there are risk factors that can increase the likelihood of developing this type of cancer. Just because someone has a risk factor does not mean they will have cancer, and not having a risk factor does not mean they will not develop cancer.

Diet

Diets that are high in red (pork, lamb, and beef) and processed meats increase the risk of rectal cancer. No relationship has been demonstrated between consumption of turkey and chicken and developing rectal cancer.

Eating fried foods or grilled meats can increase the risk.

Not eating enough fresh fruits and vegetables can also increase the risk.

Lack of physical activity

People who are not physically active are more likely to develop colorectal cancer.

Bodyweight

Excess weight may increase the risk of developing colorectal cancer, especially in men.

Smoking

Smoking increases the risk of colorectal cancer. The longer you smoke and the more cigarettes you consume, the greater the risk.

Inflammatory bowel conditions

Having an inflammatory bowel condition, such as ulcerative colitis or Crohn's disease, can increase the risk of developing colorectal cancer. People who have these conditions can participate in regular screening programs with colonoscopies.

Irritable bowel syndrome is not an inflammatory condition of the intestines and does not increase risk of developing cancer.

Family history

Most people who have colon or colorectal cancer have no family history of the disease. Having a family member who developed colon cancer at an older age does not increase your risk significantly. However, if several members of your close family have had colorectal cancer or if a member of your close family developed the disease before age 50, this may indicate a higher risk. Your close family members include your parents and siblings.

Hereditary conditions

Around 5% of cancers of the intestines are caused by an inherited genetic defect.

Two conditions may be associated with hereditary predisposition: familial adenomatous polyposis (FAP) and Lynch syndrome.

People who have either of these two conditions have a very high risk of developing colon/rectal cancer.

  • Familial adenomatous polyposis (FAP)
    People with FAP have many benign tumors (polyps) in the lining of their colon and rectum.
    It is usually recommended that people with FAP have surgery to remove the colon and, in some cases, the rectum.
    Unless the colon is removed, almost everyone with FAP will develop colon cancer.
    FAP causes about 1% of all colon cancers.
  • Lynch syndrome
    People who have Lynch syndrome are at greater risk of developing colorectal cancer at a young age. If you have Lynch syndrome, you will probably have regular tests performed using colonoscopy.
    Lynch syndrome causes about 3% of all colorectal cancers.