Patient information: Colon cancer screening

COLON CANCER SCREENING OVERVIEW

Colorectal cancer is a cancer that develops in the large intestine [colon] or rectum. The primary goal of colon cancer screening is to prevent deaths from colon cancer. Screening tests can help identify cancers at an early and potentially treatable stage. Some tests can also prevent the development of colorectal cancer by identifying precancerous abnormal growths called adenomatous polyps; these polyps can be removed before they become malignant.

All adults should undergo colon cancer screening beginning at age 50 or earlier, depending upon your risk of developing colorectal cancer. Several tests are currently available, each of which has advantages and disadvantages. The optimal screening test depends upon your preferences and your risk of developing colon cancer.

This article discusses colon cancer risks, available screening tests, and recommendations for screening based upon your risks. There are additional topics about the screening tests themselves (see "Patient information: Flexible sigmoidoscopy" and "Patient information: Colonoscopy") as well as about particular conditions (see "Patient information: Colon polyps" and "Patient information: Crohn's disease" and "Patient information: Ulcerative colitis".

EFFECTIVENESS OF COLON CANCER SCREENING

Most colorectal cancers develop from precancerous adenomatous polyps. A small percentage of these polyps become cancerous and spread to other areas. This progression takes at least 10 years in most people.

Colon cancer screening tests work by detecting polyps or by finding early stage cancers. Regular screening for and removal of polyps can reduce your risk of developing colorectal cancer by up to 90 percent. Early detection of cancers that are already present in the colon increases the chances of successful treatment and decreases the chance of dying as a result of the cancer.

COLON CANCER RISK FACTORS

Several factors increase an individual's risk of developing colorectal cancer. Having one or more of these factors will determine the age when you should begin screening, the frequency of screening, and the screening tests that are most appropriate.

Small increases in risk — Several characteristics increase the risk of colorectal cancer. While each individual risk factor adds some risk, risk is substantially increased if several are present together.

• Family history of colorectal cancer — Having colorectal cancer in a family member increases your risk of cancer, especially if the family member is a first degree relative (a parent, brother or sister, or child), if several family members are affected, or if the cancers have occurred at an early age (eg, before age 55 years). (See 'Family history of colorectal cancer' below.)

• Prior colorectal cancer or polyps — People who have previously had colorectal cancer have an increased risk of developing a new colorectal cancer. People who have had adenomatous polyps before the age of 60 years are also at increased risk for developing colorectal cancer. Screening recommendations for these groups are discussed separately. (See "Patient information: Colon polyps" and "Patient information: Colon and rectal cancer".)

• Increasing age — Although the average person has a 5 percent lifetime risk of developing colorectal cancer, 90 percent of these cancers occur in people older than 50 years of age. Risk increases with age throughout life.
• Lifestyle factors — Several lifestyle factors increase the risk of colorectal cancer, including:

• A diet high in fat and red meat and low in fiber
• A sedentary lifestyle
• Cigarette smoking

Factors that decrease risk — Factors that may decrease risk include:

• A high calcium diet — Some studies suggest that it is possible to reduce the risk of colon cancer by consuming at least 1000 mg of calcium daily, either through your diet or by taking a calcium supplement.
• Aspirin, ibuprofen, and related nonsteroidal antiinflammatory medications may decrease the risk of developing colorectal cancer. However, there is not enough evidence to recommend NSAIDs as a preventive treatment for colon cancer.

Large increase in risk — Some conditions greatly increase the risk of colorectal cancer.

Familial adenomatous polyposis — Familial adenomatous polyposis (FAP) is an uncommon inherited condition that increases the risk of colorectal cancer. Nearly 100 percent of people with this condition will develop colorectal cancer during their lifetime, and most of these cancers occur before the age of 50 years. FAP causes hundreds of polyps to develop throughout the colon. (See "Clinical features and diagnosis of familial adenomatous polyposis".)

Hereditary nonpolyposis colon cancer — Hereditary nonpolyposis colon cancer (HNPCC, also called Lynch syndrome) is another inherited condition associated with an increased risk of colorectal cancer. It is slightly more common than FAP, but is still uncommon, accounting for about 1 in 20 cases of colorectal cancer. About 70 percent of people with HNPCC will experience colorectal cancer by the age of 65. Cancer also tends to occur at younger ages. People with HNPCC are also at risk for other types of cancer, including cancer of the uterus, stomach, bladder, kidney, and ovary. (See "Clinical features and diagnosis of Lynch syndrome (hereditary nonpolyposis colorectal cancer)".)

Inflammatory bowel disease — People with Crohn's disease of the colon or ulcerative colitis have an increased risk of colorectal cancer. The amount of increased risk depends upon the amount of inflamed colon and the duration of disease; pancolitis (inflammation of the entire colon) and colitis of 10 years' duration or longer are associated with the greatest risk for colorectal cancer. The risk of colon cancer is not increased in people with irritable bowel disease.

COLON CANCER SCREENING TESTS

Several tests are available for colorectal cancer screening, including tests that can detect cancers at an early treatable stage (eg, stool tests), and tests that also detect pre-cancerous polyps (adenomas) and can lead to cancer prevention.

Guidelines from expert groups recommend that you and your healthcare provider discuss the available options and choose a testing strategy that makes sense for you. Tests that detect pre-cancerous polyps are generally preferred; these include colonoscopy, CT colonography, flexible sigmoidoscopy, and double contrast barium enema. Stool tests that detect blood or abnormal DNA are another option [1].

Colonoscopy — Colonoscopy allows a physician to see the lining of the rectum and the entire colon (figure 1). (See "Patient information: Colonoscopy".)

• Procedure — Colonoscopy requires that you prepare by cleaning out your entire colon and rectum. This usually involves consuming a liquid medication that causes temporary diarrhea. You are given a mild sedative drug before the procedure. During colonoscopy, a thin, lighted tube is used to directly view the lining of the rectum and the entire colon. Polyps and some cancers can be removed during this procedure.
• Effectiveness — Colonoscopy detects most small polyps and almost all large polyps and cancers [2].
• Risks and disadvantages — The risks of colonoscopy are greater than those of other screening tests. Colonoscopy leads to serious bleeding or a tear of the intestinal wall in about 1 in 1,000 people. Because the procedure usually requires sedation, you must be accompanied home after the procedure and you should not return to work or other activities on the same day.

CT colonography ("virtual colonoscopy") — Computed tomography colonography (CTC, sometimes called "virtual colonoscopy") is a test that uses a CT scanner to take images of the entire bowel. These images are in two- and three-dimensions, and are reconstructed to allow a radiologist to determine if polyps or cancers are present (picture 1). The major advantages of CTC are that it does not require sedation, it is non-invasive, the entire bowel can be examined, and abnormal areas (adenomas) can be detected about as well as with traditional (optical) colonoscopy.

There are several disadvantages of CTC. Like traditional colonoscopy, CTC requires a bowel prep to clean out the colon. If an abnormal area is found with CTC, a traditional colonoscopy will be needed at a later time to see the area and take a tissue sample (biopsy). CTC may detect abnormalities other than polyps and colorectal cancer. Many of these incidental findings will require further testing. This test may not be covered by health insurance plans in the United States.

Sigmoidoscopy — Sigmoidoscopy allows a physician to directly view the lining of the rectum and the lower part of the colon (the descending colon, (figure 1). This area accounts for about one-half of the total area of the rectum and colon. (See "Patient information: Flexible sigmoidoscopy".)

• Procedure — Sigmoidoscopy requires that you prepare by cleaning out the lower bowel. This usually involves consuming a clear liquid diet and using an enema shortly before the examination. Most people do not need sedative drugs and are able to return to work or other activities the same day. During the procedure, a thin, lighted tube is advanced into the rectum and through the left side of the colon to check for polyps and cancer; the procedure may cause mild cramping. Biopsies (small samples of tissue) can be taken during sigmoidoscopy. Sigmoidoscopy may be performed in a doctor's office.
• Effectiveness — Sigmoidoscopy can identify polyps and cancers in the descending colon and rectum with a high degree of accuracy. Studies suggest that sigmoidoscopy, performed periodically, reduces death from cancers in the lower half of the colon and rectum (the area directly examined) by two-thirds [3].
• Risks and disadvantages — The risks of sigmoidoscopy are small. The procedure creates a small tear in the intestinal wall in about 2 per every 10,000 people; death from this complication is rare. A major disadvantage of sigmoidoscopy is that it cannot detect polyps or cancers that are located in the right side of the colon.
• Additional testing — Finding polyps or cancers in the lower colon increase the likelihood that there are polyps or cancer in the remaining part of the colon. Thus, if sigmoidoscopy reveals polyps or cancer, colonoscopy is recommended to view the entire length of the colon.

Double contrast barium enema — A barium enema test provides a detailed x-ray picture of the rectum and the entire colon (figure 1). This test has largely been replaced by other options. Polyps or cancers cannot be removed during a barium enema, and CT colonography is more accurate for detecting abnormalities [4].

Stool tests — Colorectal cancers often bleed, releasing microscopic amounts of blood and abnormal DNA into the stool. Stool tests can detect blood or abnormal DNA makers.

Two types of tests, called guaiac tests (typically Hemoccult®) and immunochemical tests, evaluate the stool for blood, which may be present if there is bleeding from a colon cancer (or other source of blood).

• With guaiac testing, you collect two samples of stool from three consecutive bowel movements, which you apply to home collection cards. You mail the cards back to the healthcare provider. You should not consume red meat or vitamin C for 3 days before testing. You should avoid nonsteroidal antiinflammatory medications (eg, aspirin, ibuprofen, naproxen) for 7 days before testing. These medications/foods may affect the accuracy of guaiac testing.
• With immunochemical testing, you use a long handled tool to brush the surface of your stool in the toilet bowl after two consecutive bowel movements. You apply the brush to a card, and then mail the card to a laboratory. You do not have to change your diet or stop any medications with this test.
• With stool DNA testing, you collect an entire bowel movement and mail it to a laboratory with an ice pack. You do not have to change your diet or stop any medications with this test. The stool DNA test evaluates stool for several DNA markers, which can be associated with colon cancers.
• Effectiveness — Guaiac testing, when performed once per year, can reduce the risk of dying from colorectal cancer by at least one-third [5].
• Risks and disadvantages — Because polyps seldom bleed, guaiac testing is less likely to detect polyps than other screening tests. In addition, only 2 to 5 percent of people with a positive stool test actually have colorectal cancer.
• Additional testing — If the stool test is positive, your entire colon should be examined with colonoscopy.

Fecal occult blood test and sigmoidoscopy — Combined screening with a fecal occult blood test (guaiac) and sigmoidoscopy is a possible screening strategy and may be more effective than either test done alone.

COLON CANCER SCREENING PLANS

The recommended colon cancer screening plan depends upon your risk of colorectal cancer.

Average risk of colorectal cancer — People with an average risk of colorectal cancer should begin screening at age 50. The following screening strategies are recommended [1]:

• Colonoscopy every 10 years
• Computed tomographic colonography every 5 years
• Flexible sigmoidoscopy every five years
• Double contrast barium enema every five years

Stool testing is an alternate option and is recommended once per year (for guaiac and immunologic tests, less frequently for DNA-based tests). Testing should begin at age 50.

Increased risk of colorectal cancer — Screening plans for people with an increased risk may entail screening at a younger age, more frequent screening, and/or the use of more sensitive screening tests (usually colonoscopy). The optimal screening plan depends upon the reason for increased risk.

Family history of colorectal cancer

• - People who have one first-degree relative (parent, brother, sister, or child) with colorectal cancer or adenomatous polyps at a young age (before the age of 60 years), or two first-degree relatives diagnosed at any age, should begin screening for colon cancer earlier, typically at age 40, or 10 years younger than the earliest diagnosis in their family, whichever comes first. Screening usually includes colonoscopy, which should be repeated every five years. (See "Screening for colorectal cancer: Strategies in patients with possible increased risk due to family history".)
• - People who have one first-degree relative (parent, brother, sister, or child) who has experienced colorectal cancer or adenomatous polyps at age 60 or later, or two or more second degree relatives (grandparent, aunt, uncle) with colorectal cancer should begin screening at age 40, and screening should be repeated as for average risk people.
• - People with a second-degree relative (grandparent, aunt, or uncle) or third-degree relative (great-grandparent or cousin) with colorectal cancer are considered to have an average risk of colorectal cancer (see 'Average risk of colorectal cancer' above.

Familial adenomatous polyposis — People with a family history of familial adenomatous polyposis (FAP) should consider genetic counseling and genetic testing to determine if they carry the affected gene. People who carry the gene or do not know if they carry the gene should begin screening with sigmoidoscopy once every year, beginning at puberty. (See "Screening and management strategies for patients and families with familial colon cancer syndromes".)

Colectomy (surgical removal of the colon) should be considered if you have multiple polyps or genetic testing shows that you carry the abnormal gene; colectomy is the only way to prevent colorectal cancer in people with FAP.

Hereditary nonpolyposis colon cancer — People with a family history of hereditary nonpolyposis colon cancer (HNPCC) should consider genetic counseling and genetic testing to determine if they carry the affected gene. People who carry the gene or who do not know if they carry the gene should be screened with colonoscopy because HNPCC is associated with cancers of the right-sided colon (which cannot be seen during sigmoidoscopy).

Depending upon your family history and what is found, colonoscopy is usually repeated every one to two years between age 20 and 30 years, and every year after age 40. Because polyps can progress more rapidly to cancer in people with HNPCC, more frequent screening may be recommended. (See "Screening and management strategies for patients and families with familial colon cancer syndromes".)

Inflammatory bowel disease — In people with ulcerative colitis or Crohn's disease of the colon, the optimal screening plan depends upon the amount of colon affected and the duration of the disease. (See "Patient information: Crohn's disease" and "Patient information: Ulcerative colitis" and "Colorectal cancer surveillance in inflammatory bowel disease".)

WHERE TO GET MORE INFORMATION

Your healthcare provider is the best source of information for questions and concerns related to your medical problem. Because no two people are exactly alike and recommendations can vary from one person to another, it is important to seek guidance from a provider who is familiar with your individual situation.

This discussion will be updated as needed every four months on our web site (www.uptodate.com/patients). Additional topics as well as selected discussions written for healthcare professionals are also available for those who would like more detailed information.

Some of the most pertinent include:

Patient Level Information:
Patient information: Flexible sigmoidoscopy
Patient information: Colonoscopy
Patient information: Colon polyps
Patient information: Crohn's disease
Patient information: Ulcerative colitis
Patient information: Colon and rectal cancer

Professional Level Information:
Colorectal cancer surveillance in inflammatory bowel disease
Computed tomographic colonography
Gardner's syndrome
Screening for colorectal cancer: Strategies in patients at average risk
Screening for colorectal cancer: Strategies in patients with possible increased risk due to family history
Clinical features and diagnosis of familial adenomatous polyposis
Clinical features and diagnosis of Lynch syndrome (hereditary nonpolyposis colorectal cancer)
Screening and management strategies for patients and families with familial colon cancer syndromes

A number of web sites have information about medical problems and treatments, although it can be difficult to know which sites are reputable. Information provided by the National Institutes of Health, national medical societies and some other well-established organizations are often reliable sources of information, although the frequency with which they are updated is variable.

• National Cancer Institute

       1-800-4-CANCER
       (www.nci.nih.gov)

• The American Society of Clinical Oncology

      (www.cancer.net/portal/site/patient)

• National Comprehensive Cancer Network

      (www.nccn.com)

• American Cancer Society

       1-800-ACS-2345
      (www.cancer.org)

• National Library of Medicine

      (www.nlm.nih.gov/medlineplus/healthtopics.html)

• The American Gastroenterological Association

      (www.gastro.org)

• The American College of Gastroenterology

      (www.acg.gi.org)