• What is colorectal cancer?

    Colorectal (large bowel) cancer is a disease in which malignant (cancer) cells form in the inner lining of the colon or rectum. Together, the colon and rectum make up the large bowel or large intestine. The large intestine is the last segment of the digestive system (the esophagus, stomach, and small intestine are the first three sections). The large bowel's main job is to reabsorb water from the contents of the intestine so that solid waste can be expelled into the toilet. The first several feet of the large intestine is the colon and the last 6 inches is the rectum.

    Most colon and rectal cancers originate from benign wart-like growths on the inner lining of the colon or rectum called polyps or flat lesions. The difference between polyps and flat lesions is primarily just their shape, with polyps growing more into the lumen than flat lesions. Not all polyps and flat lesions have the potential to transform into cancer. Those that do have the potential are called adenomas and sessile serrated polyps (also called sessile serrated adenomas). It takes more than 10 years in most cases for a precancerous polyp or flat lesion to develop into cancer. This is why some colon cancer prevention tests are effective even if done at 10-year intervals. This 10-year interval is too long, in some cases, such as in persons with ulcerative colitis or Crohn's colitis, in persons with a strong family history of colorectal cancer or adenomas, in persons who themselves have previously had colorectal cancer, and some persons who have had precancerous polyps or flat lesions

  • How common is colorectal cancer?

    In the United States, colorectal cancer is the third most common cancer in both men and women, yet it is one of the most preventable types of cancer. The lifetime risk of colorectal cancer for men is 1 in 23 and for women is 1 in 25. An estimated 50,000+ people will die from colorectal cancer this year. It has been estimated that people born around 1990 have twice the risk of colon cancer and four times the risk of rectal cancer than those born around 1950. While the reasons for these trends are complex, experts suggest unhealthy diet and sedentary lifestyle may contribute.

Risk Factors

  • Who is at risk for colorectal cancer?
    • Average Risk Individuals
      The average age to develop colorectal cancer is 70 years, and 93% of cases occur in persons 50 years of age or older. Current recommendations are to begin screening at age 45 if there are no risk factors other than age for colorectal cancers. A person whose only risk factor is their age is said to be at average risk.
    • Men and women
      Men tend to get colorectal cancer at an earlier age than women, but women live longer so they 'catch up' with men and thus the total number of cases in men and women is equal.
    • Anyone with a family history of colorectal cancer.
      If a person has a history of two or more first-degree relatives (parent, sibling, or child) with colorectal cancer, or any first-degree relatives diagnosed under age 60, the overall colorectal cancer risk is three to six times higher than that of the general population. For those with one first-degree relative diagnosed with colorectal cancer at age 60 or older, there is an approximate two times greater risk of colon cancer than that observed in the general population. Special screening programs are used for those with a family history of colorectal cancer. A well-documented family history of adenomas is also an important risk factor.
    • Anyone with a personal history of colorectal cancer or adenomas at any age, or cancer of endometrium (uterus) or ovary diagnosed before age 50.
      Persons who have had colorectal cancer or adenomas removed are at increased risk of developing additional adenomas or cancers. Women diagnosed with uterine or ovarian cancer before age 50 are at increased risk of colorectal cancer. These groups should be checked by colonoscopy at regular intervals, usually every 3 to 5 years. Woman with a personal history of breast cancer have only a very slight increase in risk of colorectal cancer.


  • What are the symptoms of colorectal cancer?

    Symptoms of colorectal cancer vary depending on the location of the cancer within the colon or rectum, though there may be no symptoms at all. The prognosisis worse on average in symptomatic as compared to asymptomatic individuals (the latter refers to persons with cancer discovered by screening). The most common presenting symptom of colorectal cancer is rectal bleeding. Cancers arising from the left side of the colon generally cause bleeding, or in their late stages may cause constipation, abdominal pain, and obstructive symptoms. On the other hand, right-sided colon cancers may produce vague abdominal aching, but are unlikely to present with obstruction or altered bowel habit. Other symptoms such as weakness, weight loss, or anemia resulting from chronic blood loss may accompany cancer of the right side of the colon. You should promptly see your doctor when you experience any of these symptoms.

  • Why should you get checked for colorectal cancer even if you have no symptoms?

    Precancerous polyps and flat lesions can grow for years and transform into cancer without producing any symptoms. By the time symptoms develop, it is often too late to cure the cancer, because it may have spread. Screening identifies cancers earlier and actually results in cancer prevention when it leads to removal of pre-cancerous growths


  • What is screening for colorectal cancer?

    Screening means looking for cancer or polyps when patients have no symptoms. Finding colorectal cancer before symptoms develop dramatically improves the chance of survival. Identifying and removing polyps before they become cancerous actually prevents the development of colorectal cancer.

  • What tests are available for screening?

    Several options are available for screening average-risk persons.

    • Colonoscopy
      Your doctor can examine your entire colon and rectum during colonoscopy. The procedure is used to look for early signs of cancer in the colon and rectum where they could not be reached by sigmoidoscopy. Polyps and flat lesions can be removed during colonoscopy. Sedation is usually used for colonoscopy. Colonoscopy is currently the only test recommended for colorectal cancer screening in average-risk persons at 10 year intervals
    • Flexible Sigmoidoscopy
      An examination in which a doctor uses a sigmoidoscope (a thin, lighted instrument) to view the inside of the lower colon and rectum (usually about the lower 2 feet) for polyps and cancers. If a precancerous growth is found, colonoscopy should be performed. Sigmoidoscopy does not examine the entire colon and so is less reliable than colonscopy for detecting polyps and flat lesions. Sedation is usually not used for sigmoidoscopy. Sigmoidoscopy is performed every 5 years, often in conjunction with an annual fecal occult blood test.
    • Fecal occult blood test
      One of the presentations of colon cancer is chronic blood loss in the stool. Sometimes, such blood loss is so minimal, it cannot be seen when the stool is inspected in the toilet. Your doctor will ask you to collect a stool sample which is returned to the doctor or lab to test for occult (hidden) blood. There are two types of tests, called the fecal immunochemical test (FIT) and the guaiac test. The fecal immunochemical test (FIT) is the better test. Either test is done annually. If either test is positive, colonoscopy should be done
    • Computerized topographic (CT) colonography and magnetic resonance (MR) colonography
      These tests are sometimes called "Virtual Colonoscopy". These two tests are fairly new methods that allow your doctor to look for colorectal polyps and cancers. Virtual Colonoscopy uses a CT scanner (CT colonography) or Magnetic Resonance scanner (MR colonography) along with computer-assisted software to look inside the body without having to insert a long colonoscope into the colon or without having to fill the colon with liquid barium. These two tests are performed by radiologists. The US Preventive Services Task Force and the Centers for Medicare and Medicaid Services do not endorse CT colonography or MR colonography for screening, so they may not be covered by your insurance program.
    • Fecal DNA testing
      Colorectal cancers contain abnormal DNA which is shed into the stool. In this a sample of stool is checked for abnormal DNA and colonoscopy is performed if any is found. This test should be repeated at 3 years if it’s negative.


  • What else can I do to prevent the development of colorectal cancer?

    The strategy for reducing colorectal cancer deaths is simple.

    • CRC screening at age 45 in average risk individuals and using either colonoscopy or fecal immunochemical test (FIT) as the primary screening modality. Other screening options include multitarget stool DNA test, CT colonography, and colon capsule.
    • For higher risk patients with a family history of colorectal cancer, screening should begin at age 40 in individuals with one first degree relative with colorectal cancer or advanced colorectal polyp. If the first degree relative is <60, colonoscopy should be used, and screening repeated at five-year intervals. If the first degree relative is age 60 or older, any screening modality can be used and, if normal, follow average risk screening intervals. For individuals with one second degree relative, we suggest using average risk recommendations.
    • For both average and high risk individuals, all potential pre-cancerous polyps should be removed.

    Aspirin is not a substitute for colorectal cancer screening and we suggest a narrow category of individuals that may use aspirin, in addition to routine screening, to reduce their risk of colorectal cancer: persons that are age 50-69 with cardiovascular disease risk of at least 10% and willing to take aspirin for at least 10 years.

Author(s) and Publication Date(s)

Suthat Liangpunsakul, MD and Douglas K. Rex, MD, FACG, Indiana University School of Medicine, Indianapolis, IN – Published October 2002.

Suthat Liangpunsakul, MD and Douglas K. Rex, MD, FACG, Indiana University School of Medicine, Indianapolis, IN – Updated April 2007. Updated December 2012.

Reviewed in 2021 in light of publication of 2021 ACG Clinical Guidelines on Colorectal Cancer Screening (Shaukat, et al.) – March 2021.

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