Colorectal Cancer Screening
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
Colorectal cancer is the second most common cancer killer
overall and third most common cause of cancer-related death in the United
States in both males and females. Lung and prostate cancers are more common in
men and lung and breast in women. In 2012, there will be 143,000 new cases and
52,000 deaths from colorectal cancer. About 6% of persons who reach the age of
50 in the United States will develop colorectal cancer without screening.
§ Everyone age 50 and older.
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 50 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.
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.
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
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.
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.
§ Double contrast barium enema (DCBE)
Barium is a white liquid that helps to show the inside image of the colon and
rectum on an X-ray. The liquid barium is put into the colon using a rectal
tube. Multiple X-rays are taken to look for polyps or cancers. DCBE is less
expensive than colonoscopy but also less effective. DCBE has not been
established as a reliable colorectal cancer screening test in any rigorous
scientific studies. One scientific report, the National Polyp Study, found that
DCBE detected only 50% of the larger adenomas (greater than 1 cm), and DCBE is
inferior to colonoscopy for detection of colorectal polyps. Because of its
limitations, DCBE is not widely used for colorectal cancer screening. If used
for screening, it should be done every 5 years. If polyps are found,
colonoscopy should be performed. Another X-ray test, single contrast barium
enema (SCBE) is generally considered inferior to DCBE for detecting polyps and,
thus, SCBE is not recommended for colorectal cancer screening.
§ 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.
The strategy for reducing colorectal cancer deaths is
simple.
§ For normal risk individuals, screening tests begin at age 50
and the preferred approach is a screening colonoscopy every 10 years; an
alternate strategy consists of annual stool test for blood and a flexible
sigmoidoscopy every 5 years.
§ Colonoscopic surveillance (also called screening colonoscopy)
needs to be available at more frequent intervals for individuals at high risk
for colon cancer (for instance, those with a personal history of colorectal
cancer or adenomatous polyps; family history of colorectal cancer; Hereditary
Non-polyposis Ccolorectal Cancer; or a pre-disposing condition such as
inflammatory bowel disease. (Medicare provides for surveillance colonoscopy no
more frequently than once every two years for those at high risk.)
§ For both average and high risk individuals, all potential
pre-cancerous polyps should be removed.
Recent observations suggest regular use of non-steroidal
anti-inflammatory drugs or aspirin, reduce the chances of colorectal cancer
death by 30-50%. These drugs also have risks, particularly intestinal bleeding,
and patients should consult their physician as to whether regular use of these
agents is appropriate. Folate, calcium, and post-menopausal estrogens each have
a modest protective benefit against colon cancer. A normal blood level of
Vitamin D is associated with lower risk of colorectal cancer. A diet high in
fiber and fruits and vegetables and low in fat diet, regular exercise,
maintenance of normal body weight and cessation of smoking are also beneficial.
None of the measures is as effective as or should replace colorectal cancer
screening.
Author(s) and Publication Date(s)
Douglas K. Rex, MD, FACG, Division
of Gastroenterology and Hepatology, Department of Medicine Indiana University
School of Medicine, Indianapolis, Indiana
– Updated April 2007. Updated December 2012.
Suthat Liangpunsakul, MD and Douglas
K. Rex, MD, FACG, Indiana University School of Medicine, Indianapolis, IN – Published October 2002.