Tests to Detect Colorectal Cancer and Polyps

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Review the different types of test used to detect colon cancer and polyps.
Review the different types of test used to detect colon cancer and polyps.

Key Points

  • Expert groups recommend that people at average risk for colorectal cancer start regular screening at age 50.
  • Current colorectal cancer screening tests check for blood in stool (high-sensitivity fecal occult blood tests) or use an instrument to look at the lining of the colon and rectum (sigmoidoscopy and colonoscopy).
  • People should talk with their health care provider about when to begin screening for colorectal cancer, what test(s) to have, the advantages and disadvantages (including potential harms) of each test, and how often to undergo screening.
  • New methods of screening for colorectal cancer, such as virtual colonoscopy and tests that analyze human DNA in stool or blood samples for certain changes, are under study.

What is colorectal cancer?

Colorectal cancer is a disease in which abnormal cells in the colon or rectum divide uncontrollably, ultimately forming a malignant tumor. (The colon and rectum are parts of the body's digestive system, which takes up nutrients from food and water and stores solid waste until it passes out of the body.)

Most colorectal cancers begin as a polyp, a growth in the mucous tissue that lines the inner surface of the colon or rectum. Polyps may be flat, or they may be raised. Raised polyps may grow on the inner surface of the colon or rectum like mushrooms without a stalk (sessile polyps), or they may grow like a mushroom with a stalk (pedunculated polyps). Polyps are common in people older than 50 years of age, and most are benign (noncancerous). However, a certain type of polyp known as an adenoma may develop into cancer.

Colorectal cancer is the third most common type of non-skin cancer in both men (after prostate cancer and lung cancer) and women (after breast cancer and lung cancer). It is the second leading cause of cancer death in the United States after lung cancer.

Although the rates of new colorectal cancer cases and deaths among adults aged 50 years or older are decreasing in this country, incidence is increasing among younger adults (1). It is estimated that in 2014, a total of 136,830 people in the United States will be diagnosed with colorectal cancer and 50,310 people will die from it (1).

Although the major risk factor for colorectal cancer is older age, several other factors have been found to be associated with increased risk, including excessive alcohol use, obesity, being physically inactive, cigarette smoking, and possibly diet.

In addition, people with a history of inflammatory bowel disease (such as ulcerative colitis or Crohn disease) have a higher risk of colorectal cancer than people without such conditions. And people who have a family history of colorectal cancer or certain inherited conditions (such as Lynch syndrome and familial adenomatous polyposis) also have an increased risk of colorectal cancer. (More information about risk factors for colorectal cancer is available in NCI's PDQ summary on Colorectal Cancer Screening.)

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