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Diseases & Conditions

Colorectal Cancer - Prevention

How does colorectal cancer form?

Colorectal cancer occurs because of genetic changes in the colon lining that let to precancerous growths called adenomatous polyps. If adenoma (a type of polyp) is left to grow large, it can turn into colorectal cancer. Factors that are associated with genetic changes include:

  • Increasing age
  • Obesity
  • Low fruit-vegetable-fiber diet
  • Smoking
  • Diets high in processed meats and fats

What are the symptoms of colorectal polyps and cancer?

Unfortunately, the majority of colorectal polyps and early cancers do not cause symptoms. This is why it is important to have colon cancer screening before symptoms develop. Symptoms of large polyps or cancer usually include some form of bleeding, either:

  • Bleeding that can be seen with a bowel movement, or
  • Microscopic bleeding that can lead to anemia or low red blood cell count

Other potential symptoms of colorectal cancer include:

  • Abdominal pain
  • Change in bowel habits
  • Unexplained weight loss

Is colorectal cancer preventable?

Yes. It has been shown that detecting and removing precancerous polyps can prevent colorectal cancer. In addition, through routine colorectal cancer screening with colonoscopy, fecal occult blood testing (FOBT), and flexible sigmoidoscopy, even if cancer develops, early stage tumors can be cured. Screening is the best way to prevent deaths due to colorectal cancer.

Who is at risk of colorectal cancer?

We are all at risk of developing colorectal cancer. More than 75% of patients who get colorectal cancer have no identifiable risk factors. This group of patients is at "average risk." The remainder of patients has either a personal history of colorectal polyps or cancer, ulcerative or Crohn's colitis, or a strong family history of colorectal cancer. These patients are at "moderate to high risk."

When we say a strong family history, we mean a family that contains multiple relatives or first-degree relatives (parent, brother/sister, or child) with colorectal cancer. The risk is particularly strong if the first-degree relative with cancer was younger than age 50.

Many organizations endorse colorectal cancer screening as an effective method to reduce colorectal cancer. There is a variety of options available for colorectal cancer screening. Patients without risk factors or symptoms of colorectal cancer should discuss with their physician the screening strategy that is best for them. Patients with symptoms or risk factors suggestive of colorectal cancer should have a colonoscopy.

Average risk

People without symptoms or any risk factors for colorectal cancer are considered at average risk of developing colorectal cancer. They should begin screenings at age 50. While colonoscopy is the preferred strategy by most experts, other endorsed options include:

  • Fecal occult blood testing every year
    This is a test on smears of stool. It can detect microscopic blood through a chemical reaction. Patients should be on a specialized diet before this test is performed to try to minimize falsely positive or negative tests. The dietary restrictions include:
    • No red meat, poultry, certain raw vegetables, or melons
    • No anti-inflammatory medications or aspirin for 7 days
    • No vitamin C (or multivitamins with vitamin C)

    The test is positive if any of six windows change to a blue color. If it is positive, a colonoscopy should be performed.

    • Flexible sigmoidoscopy every 5 years
      In this test, a physician passes a thin, flexible tube into the lower colon and examines the lining. It is done in addition to the yearly fecal occult blood testing. If an adenoma is found during the flexible sigmoidoscopy, a colonoscopy should be performed to remove the polyp and search for polyps higher in the colon. It is recommended that flexible sigmoidoscopy be combined with an annual FOBT.
    • Barium enema plus sigmoidoscopy
      A barium enema is an X-ray. It is not accurate enough to check for colorectal polyps and can even miss cancers. It should not be used for colorectal cancer screening unless a colonoscopy cannot be performed. If it is used, it should be coupled with a flexible sigmoidoscopy to see the part of the lower colon that is not well seen on X-ray.
    • Colonoscopy every 10 years
      During a colonoscopy, the doctor inserts a thin flexible tube into the complete colon. If the examination is normal, this test is done every 10 years. Colonoscopy is the preferred colorectal cancer screening test. It is also the test of choice if patients have any symptoms that could be suggestive of colorectal cancer such as intestinal bleeding, unexplained abdominal pain, or change in bowel habits. No additional FOBT or sigmoidoscopy should be done between colonoscopy examinations. If any polyps are seen during the exam, they should be removed and sent to the laboratory for analysis. If adenomas are found, a follow-up colonoscopy generally is performed in 3 to 5 years. Many patients with adenomas require lifelong colonoscopy at 3- to 5-year intervals.
    Moderate risk

    People who are at moderate risk of developing colorectal cancer have a personal history of adenomatous polyps or colorectal cancer; one first-degree relative (parent, child, or sibling) with colorectal cancer or adenoma before the age of 50; or more than one first-degree relative with colorectal cancer at any age.


    • Colonoscopy every 5 years
    • Start at age 40, or 10 years before the youngest case in the family, whichever is earlier
    High risk

    People with an inherited predisposition to colorectal cancer, such as familial adenomatous polyposis (FAP) or hereditary nonpolyposis colorectal cancer (HNPCC), are considered at high risk for developing colorectal cancer. A team of experts familiar with the diagnosis and treatment of these disorders should see them and their family members.



    • Flexible sigmoidoscopy or colonoscopy every 6 to 12 months, starting in puberty
    • Refer to Cleveland Clinic Medical Genetics Program at 216.445.5686 and the High Risk Clinic and Inherited Colorectal Cancer Registry at 216.444.6470


    • Flexible Families with HNPCC have at least three relatives with colorectal cancer, one of whom is a first-degree relative of the other two
    • The cancer occurs over two generations
    • At least one relative must be diagnosed with colorectal cancer before age 50
    • These families may also have uterine, ovarian, or other gastrointestinal or urinary cancers


    • Colonoscopy every two years until age 40, then every year thereafter
    • Start at age 25, or 10 years younger than the youngest case in the family
    • Pelvic ultrasound and endometrial biopsy every year beginning at age 25
    • Refer to Cleveland Clinic Medical Genetics Program at 216.445.5686 and the High Risk Clinic and Inherited Colorectal Cancer Registry at 216.444.6470

    Inflammatory bowel disease (Crohn's or ulcerative colitis)

    People with inflammatory bowel disease (IBD) should have a colonoscopy with biopsy for dysplasia every 1 to 2 years. Colonoscopies should start 8 years after the onset of symptoms if the whole colon has been inflamed (pancolitis) and 12 years after the onset of symptoms if only the left side of the colon has been inflamed.


    Report of the U.S. Preventive Services Task Force. Guide to Clinical Preventive Services. Baltimore, MD: Williams & Wilkins, 1996.

    Winawer S, Fletcher R, Rex D, et al. Gastrointestinal Consortium Panel. Colorectal Cancer Screening and Surveillance: Clinical Guidelines and Rationale—Update based on new evidence. Gastroenterology 2003;124:544-60.

    Smith RA, Cokkinides V, Eyre HJ. American Cancer Society Guidelines for the Early Detection of Cancer, 2004. Ca: a Cancer Journal for Clinicians 2004;54(Jan-Feb):41-52.

    Ransohoff, DF, Lang CA. Clinical Guideline: Part I and Part II. Ann Intern Med 1997;126:808-822.

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    This information is provided by the Cleveland Clinic and is not intended to replace the medical advice of your doctor or health care provider. Please consult your health care provider for advice about a specific medical condition. This document was last reviewed on: 3/4/2008...#8172