Screening for colon cancer - Gastro Services and Facilities

GASTRO SERVICES & FACILITIES
PATIENT INFORMATION: SCREENING FOR COLON CANCER
INTRODUCTION — Colorectal cancer is a cancer of the large portion of the bowel [colon] or
rectum. These cancers are common and deadly; approximately one-third of people who
develop it die, making it the second leading cause of cancer death. However, screening tests
make it possible to detect existing cancers at an early, treatable stage, before there are any
symptoms. Screening tests can also help to prevent the development of colorectal cancer by
identifying and removing early growths called adenomatous polyps.
All adults should undergo screening beginning at age 50 or earlier, depending upon a
person's risk of developing colorectal cancer. Several different tests are currently available,
and new tests are being developed; all of these tests have advantages and disadvantages.
The optimal screening test depends upon a person's preferences and their risk of
developing colon cancer.
This topic review discusses risk groups, available screening tests, and recommendations for
screening based upon a person's risk. There are additional topics about the screening tests
themselves (see "Patient information: Flexible sigmoidoscopy" and see "Patient
information: Colonoscopy") as well as about particular conditions (see "Patient information:
Colon polyps" and see "Patient information: Crohn's disease" and see "Patient information:
Ulcerative colitis").
EFFECTIVENESS OF SCREENING — Most colorectal cancers develop slowly 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.
Colon cancer screening tests work by detecting cancer while it is 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 increases the chances of successful treatment and decreases the chance of dying
as a result of the cancer.
WHO SHOULD BE SCREENED? — Several factors increase an individual's risk of developing
colorectal cancer. Having one or more 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 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 the risk of getting the cancer, especially if it 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).
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. (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 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 may decrease risk include:
A high calcium diet — The risk of colon cancer may be decreased by consuming at least
1000 mg of calcium daily, either through 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 a person's 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, 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 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 cancer of the uterus,
stomach, bladder, kidney, and ovary.
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.
Risk is not increased in people with irritable bowel disease.
SCREENING TESTS — Four tests are currently recommended for colorectal cancer
screening: the faecal occult blood test, sigmoidoscopy, double contrast barium enema, and
colonoscopy.
Faecal 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 faecal 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 reduce the chance of a
false positive test. These include:
Eliminate red meat, turnips, and horseradishes Avoid drugs that may irritate the stomach
lining (such as aspirin, ibuprofen-like drugs)
Vitamin C can cause a false negative test and should be avoided
Eat high-fiber foods Effectiveness — The faecal occult blood test, when performed once
every year, has been shown to reduce the risk of dying from colorectal cancer by up to onethird
[1].
Risks and disadvantages — Because polyps seldom bleed, the faecal 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 undergo tests that eventually reveal
no cancer. Following the dietary restrictions above reduces the chance of a false-positive
test. Additional testing — If a faecal 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. (See "Patient information: Flexible

sigmoidoscopy"). Procedure — Sigmoidoscopy requires that the patient prepare by cleaning
out the lower 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. 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 two-thirds [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 only in the right side of the colon. Additional testing — Finding polyps or
cancers in the lower colon increase the likelihood of polyps or cancer in the remaining part
of the colon. Thus, if sigmoidoscopy reveals polyps or cancer, colonoscopy may be
recommended to view the entire length of the colon.
Faecal occult blood test and sigmoidoscopy — Combined screening with a faecal occult
blood test and sigmoidoscopy is a common practice and may be more effective than
screening with either test alone [3].
Colonoscopy — Colonoscopy allows a physician to see the lining of the rectum and the
entire colon. (See "Patient information: Colonoscopy").
Procedure — Colonoscopy requires that the patient prepare by cleaning out the the entire
colon and rectum. This usually involves consuming a liquid that causes diarrhea
temporarily. The patient is 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 [4].
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, the person must be
accompanied home after the procedure and the person should not 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. A more accurate version of the test, called double-contrast barium
enema, is usually recommended.

Procedure — During a double contrast barium enema test, liquid barium is inserted into
the rectum where it coats the inside of the colon. The barium is then drained out and the
colon is filled with air. A thin layer of barium is left on the colon wall, which allows x-ray
images to show a detailed view of the colon wall, including structural abnormalities such as
polyps and cancers. Preparation for a barium enema including cleaning the colon by
drinking a saline laxative. Some people experience mild cramping during the procedure.
Sedative drugs are usually not necessary and most people can return to work or other
activities after the test is completed. 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 is
usually recommended.
New tests — Several new screening tests for colorectal cancer are being developed and
evaluated. These tests include improved faecal occult blood tests, faecal 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. The major advantages of virtual colonoscopy
compared with traditional 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 to see the area and remove a tissue sample (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.
Virtual colonoscopy, like traditional colonoscopy, requires cleaning out the entire colon.
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 for all adults. The available options should be discussed with a clinician to develop
a screening plan that will be followed.
Some clinicians recommend a faecal 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 colonoscopy once every 10 years or a double contrast
barium enema every five years. If the results of one or more of these tests are abnormal,
more frequent testing 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) 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.
- 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.
Colectomy (surgical removal of the colon) should be considered if multiple polyps are seen
or genetic testing shows that the person carries 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 the 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.
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 inflammation of the entire colon or after 15 years of colitis of
the sigmoid colon and rectum. (See "Patient information: Crohn's disease" and see "Patient
information: Ulcerative colitis").

REFERENCES
1. Mandel, JS, Bond, JH, Church, TR, et al. Reducing mortality from
colorectal cancer by screening for faecal 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 faecal 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.
6. Winawer, S, Fletcher, R, Rex, D, et al. Colorectal cancer screening and
surveillance: Clinical guidelines and rationale-Update based on new
evidence. Gastroenterology 2003; 124:544.
GASTRO SERVICES & FACILITIES
DR JOHN GIBBONS, DR KATE CAYZER, DR GEORGIA HUME, DR JILLIAN ROSENSTENGEL
CONSULTANT GASTROENTEROLOGISTS
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BIRKDALE QLD 4159
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