Screening for colon cancer

INTRODUCTION — Colorectal cancer (cancer of the large portion of the bowel [colon] or rectum) is a common, preventable disease. Approximately one-third of people who develop it die of the disease, making it the second leading cause of cancer death. However, screening tests now make it possible to detect existing cancers at an early, treatable stage and even to prevent the development of colorectal cancer.

There is general agreement by experts that all adults should undergo screening beginning at age 50, or earlier for people who are at high risk for colorectal cancer. Several different tests are currently available, and new tests are being developed; all of these have advantages and disadvantages. The optimal screening test depends upon a person's preferences and their risk of colon cancer. It is important to review each test's effectiveness, safety, convenience, and costs.

EFFECTIVENESS OF SCREENING — Most colorectal cancers develop gradually over many years. They begin as small, benign tumors called adenomatous polyps. These polyps grow, develop precancerous changes, eventually become cancerous, and later spread and become incurable. This progression takes at least 10 years in most people.

The screening tests described below all work by detecting pre-cancers at the polyp stage before they become cancerous or by detecting cancers themselves while they are still curable. Regular screening for and removal of polyps can reduce a person's risk of developing colorectal cancer by up to 90 percent. In addition, early detection of cancers that are already present in the colon often allows for successful treatment.

WHO SHOULD BE SCREENED? — Several factors increase an individual's risk of developing colorectal cancer. The presence of these factors will determine the age at which screening should begin, the frequency of screening, and the screening tests that are most appropriate.

Small increases in risk — Several characteristics increase the risk of colorectal cancer two to several fold. While each is of some importance individually, risk can be substantially increased if several are present together. Family history of colorectal cancer — The occurrence of colorectal cancer in a family member increases the risk of getting the cancer, especially if it is a first degree relative (a parent, brother or sister, or child), several family members are affected, or if the cancers have occurred at an early age (eg, before age 55 years). 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 colorectal cancer. (See "Patient information: Colon polyps"). 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 throughout life. Race — Black Americans have a higher risk of dying from colorectal cancer than white Americans. This risk is also high in native Alaskans and low in American Indians. Lifestyle factors — Several lifestyle factors have been linked to the risk of colorectal cancer. Factors that appear to increase risk include: A diet high in fat and red meat and low in fiber A sedentary lifestyle Cigarette smoking

Factors that may decrease risk include: Folic acid supplements Calcium supplements Aspirin, ibuprofen, and related drugs (the evidence for these is not yet strong enough to recommend taking them for this purpose)

Large increase in risk — Some conditions are associated with very high rates of colorectal cancer. Familial adenomatous polyposis — Familial adenomatous polyposis (FAP) is an uncommon inherited condition associated with an increased 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. Hereditary nonpolyposis colon cancer — Hereditary nonpolyposis colon cancer (HNPCC) is another inherited condition associated with an increased risk of colorectal cancer. It is slightly more common than FAP, but is still uncommon. About 70 percent of people with HNPCC will experience colorectal cancer by the age of 65. Cancer also tends to occur at younger ages and in the part of the colon on the right side of the body (the ascending colon).

HNPCC is suspected in those with a strong family history of colon cancer; several family members from different generations may have been affected, some of whom developed the cancer relatively early in life. Persons with HNPCC are also at risk for other types of cancer, including endometrial (uterine), stomach, bladder, renal (kidney) and ovarian cancer. Inflammatory bowel disease — The risk of colorectal cancer is increased in people with Crohn's disease of the colon or ulcerative colitis. The risk increases as the amount of inflamed colon increases and as the duration of disease increases; pancolitis (inflammation of the entire colon) and colitis of 10 years' duration or longer are associated with the greatest risk for colorectal cancer. Risk is not increased in irritable bowel disease.

SCREENING TESTS — Four tests are currently recommended for colorectal cancer screening: the fecal occult blood test, sigmoidoscopy, barium enema, and colonoscopy.

Fecal occult blood test — Colorectal cancers (and, more rarely, polyps) often bleed, releasing microscopic amounts of blood into the stool. The blood is frequently not visible to the naked eye, requiring specialized tests for detection. The fecal occult blood test can be used to detect blood in the stool. Procedure — This simple test is performed by putting small amounts of stool on chemically coated cards. Usually, two samples from three consecutive stools are applied to the cards at home and returned to the clinician. The sample on the card is then treated with a solution that changes color when blood is present.

Some simple dietary restrictions for two days prior to testing can improve the accuracy of the test. These include: Eliminate red meat, turnips, and horseradishes Avoid drugs that may irritate the stomach lining (such as aspirin, ibuprofen-like drugs) Do not take vitamin C Eat high-fiber foods Effectiveness — The fecal occult blood test, when performed once every year, has been shown to reduce the risk of dying from colorectal cancer by up to one-third [1]. Risks and disadvantages — Because polyps seldom bleed, the fecal occult blood test is less likely to detect polyps than other screening tests (see below). In addition, only 2 to 5 percent of people with a positive test actually have colorectal cancer; thus, for every patient with cancer, 50 patients are unnecessarily distressed and undergo tests that eventually reveal no cancer. Following the dietary restrictions above reduces the chance of a false-positive test. Additional testing — If a fecal occult blood test has a positive result, the entire colon should be examined, usually with colonoscopy.

Sigmoidoscopy — Sigmoidoscopy allows direct viewing of the lining of the rectum and the lower part of the colon (the descending colon, show figure 1). This area accounts for about one-half of the total area of the rectum and colon, where half of the cancers occur. (See "Patient information: Flexible sigmoidoscopy"). Procedure — Sigmoidoscopy requires that the patient prepare by cleaning out the bowel. This usually involves consuming a clear liquid diet, laxatives, and using an enema shortly before the examination. During the procedure, a thin, lighted tube is advanced into the rectum and the left side of the colon to check for polyps and cancer. Biopsies (small samples of tissue) can be removed during sigmoidoscopy. Sigmoidoscopy may be performed in a doctor's office. The procedure may cause mild cramping; most people do not need sedative drugs and are able to return to work or other activities the same day. Effectiveness — Physicians who perform sigmoidoscopy can identify polyps and cancers in the descending colon and rectum with a high degree of accuracy. Studies suggest that sigmoidoscopy, performed as infrequently as every 5 to 10 years, reduces death from cancers in the lower half of the colon and rectum (the area directly examined) by 66 percent [2]. Risks and disadvantages — The risks of sigmoidoscopy are small. The procedure can create 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 located in the right side of the colon. Additional testing — Certain changes in the left-sided colon increase the likelihood of polyps or cancer in the remaining part of the colon. Thus, if sigmoidoscopy reveals suspicious findings in the left-sided colon, such as many small polyps or polyps with certain microscopic features, colonoscopy may be recommended to view the entire length of the colon.

Fecal occult blood test and sigmoidoscopy — Combined screening with a fecal occult blood test and sigmoidoscopy is a common practice and may be more effective than screening with either test alone [3].

Colonoscopy — Colonoscopy allows direct viewing of the lining of the rectum and the entire colon (show figure 1). (See "Patient information: Colonoscopy"). Procedure — During colonoscopy, a thin, lighted tube is used to directly view the lining of the rectum and the entire colon. This test can therefore detect polyps and cancers that are beyond the reach of the sigmoidoscope. People are usually given a mild sedative drug during the procedure. Effectiveness — Colonoscopy detects most small polyps and almost all large polyps and cancers [4]. Polyps and some cancers can be removed during this procedure. 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 requires sedation, most people must be accompanied home after the procedure and are unable to return to work or other activities on the same day.

Barium enema test — A barium enema test provides a detailed x-ray picture of the rectum and the entire colon (show figure 1). A double-contrast barium enema is usually recommended. Procedure — During a barium enema test, liquid barium is used to coat the inside of the colon. The barium outlines the profile of the colon on x-rays and can reveal structural abnormalities such as polyps and cancers. Preparation for a barium enema entails cleansing the colon with a saline laxative. Some people experience mild cramping during the procedure, but sedative drugs are usually not necessary, and most people can return to work or other activities on the same day. Effectiveness — The barium enema test detects about one-half of large polyps and about 40 percent of all polyps in the colon and rectum [5]. Most experts feel that screening with barium enema reduces the risk of dying from colorectal cancer, but this has not been definitively proven. Risks and disadvantages — The barium enema test is relatively safe compared with other screening tests for colorectal cancer. Additional testing — If a barium enema test reveals an abnormality, a colonoscopy may be recommended.

New tests — Several new screening tests for colorectal cancer are being developed and evaluated. These tests include improved fecal occult blood tests, fecal tests for genetic abnormalities linked to colorectal cancer, and a type of computed tomography (CT) scan called a virtual colonoscopy. These tests are still being studied, and they are not yet recommended for routine screening.

Virtual colonoscopy, in particular, is being performed more commonly. The major advantages of virtual colonoscopy compared with optical colonoscopy are that the procedure is safe, and there is no need for sedation. However, if a worrisome polyp is found on virtual colonoscopy, a traditional colonoscopy will be needed for confirmation and biopsy. Additionally, the accuracy of virtual colonoscopy depends upon how it is performed; the test that is currently available may not be accurate enough for use as a screening test.

SCREENING PLANS — The screening plan that is recommended depends upon a person's risk of colorectal cancer.

Average risk of colorectal cancer — People with an average risk of colorectal cancer should begin screening at age 50. The tests differ in features (effectiveness in preventing cancer, comfort, safety, cost, and convenience). No single screening test has been identified as the best test. The available options should be discussed with a clinician to develop a screening plan that can be followed.

Some clinicians recommend a fecal occult blood test once per year and a sigmoidoscopy once every five years; a combination of these screening tests may also be recommended. Alternative screening plans include a barium enema test once every five years or colonoscopy once every 10 years. If the results of one or more of these tests is abnormal, more frequent examinations with colonoscopy may be recommended.

Increased risk of colorectal cancer — Screening plans for people with an increased risk may entail screening at a younger age, more frequent screening, and the use of more sensitive screening tests (like 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) who has experienced 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 earlier, typically at age 40, or 10 years younger than the earliest diagnosis in their family, whichever comes first, and screening should be repeated every five years.

- 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. If this screening reveals many polyps, plans for colectomy (surgical removal of the colon) should be considered; this surgery 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 or barium enema because HNPCC is associated with cancers of the right-sided colon. This screening should be done once every one to two years between age 20 and 30 years, and once every year after age 40. Because polyps can progress more rapidly to cancer in people with HNPCC, more frequent screening may also be recommended.

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. Screening usually entails colonoscopy once every one to two years beginning after eight years of pancolitis (inflammation of the entire colon) or after 15 years of colitis of the left-sided colon. (See "Patient information: Crohn's disease" and see "Patient information: Ulcerative colitis").

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 patients 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.patients.uptodate.com). Additional topics as well as selected discussions written for healthcare professionals are also available for those who would like more detailed information.

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)
People Living With Cancer: The official patient information

website of the American Society of Clinical Oncology
(www.plwc.org/portal/site/PLWC)
National Comprehensive Cancer Network

(www.nccn.org/patients/patient_gls.asp)
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)


[1-5]


Use of UpToDate is subject to the Subscription and License Agreement. REFERENCES 1. Mandel, JS, Bond, JH, Church, TR, et al. Reducing mortality from colorectal cancer by screening for fecal occult blood. Minnesota Colon Cancer Control Study. N Engl J Med 1993; 328:1365.
2. Selby, JV, Friedman, GD, Quesenberry, CP Jr, Weiss, NS. A case-control study of screening sigmoidoscopy and mortality from colorectal cancer. N Engl J Med 1992; 326:653.
3. Winawer, SJ, Flehinger, BJ, Schottenfeld, D, Miller, DG. Screening for colorectal cancer with fecal occult blood testing and sigmoidoscopy. J Natl Cancer Inst 1993; 85:1311.
4. Rex, DK, Cutler, CS, Lemmel, GT, et al. Colonoscopic miss rates of adenomas determined by back-to-back colonoscopies. Gastroenterology 1997; 112:24.
5. Winawer, SJ, Stewart, ET, Zauber, AG, et al. A comparison of colonoscopy and double-contrast barium enema for surveillance after polypectomy. National Polyp Study Work Group. N Engl J Med 2000; 342:1766.