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By Douglas K. Rex, M.D., FACG & Suthat
Liangpunsakul, M.D.
Division of Gastroenterology and Hepatology, Department of
Medicine
Indiana University School of Medicine
Indianapolis, Indiana
Originally published in October 2002. Updated by Douglas K. Rex, M.D., FACG in April 2007.
1. What is colorectal cancer?
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. Not all polyps have the potential to transform into
cancer. Those that do have the potential are called adenomas.
It takes more than 10 years in most cases for an adenoma
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, and in persons
with a strong family history of colorectal cancer or adenomas.
2. How common is colorectal cancer?
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 2007, there will be 153,000 new cases and 52,000
deaths from colorectal cancer.
3. What is screening for colorectal cancer?
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.
4. Who is at risk for colorectal cancer?
- 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.
4. What are the symptoms 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 prognosis tends to be worse in
symptomatic as compared to asymptomatic individuals. 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 lesions 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.
5. Why should you get checked for colorectal
cancer even if you have no symptoms?
Adenomas 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 adenomas (pre-cancerous polyps).
6. What tests are available for screening?
Several options are available for screening average-risk
persons.
- 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 guaiac test and the immunochemical
test. The fecal immunochemical test is the better test. Either test is
done annually. If either test is positive, colonoscopy should be done.
- 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.
- 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 an adenoma is found, colonoscopy should
be performed. Sigmoidoscopy does not examine the entire colon and so is
less reliable than colonscopy for detecting polyps. Sedation is usually
not used for sigmoidoscopy. Sigmoidoscopy is performed every 5 years, often
in conjunction with an annual fecal occult blood test.
- 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 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.
- 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 is a recently developed technique
that 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.
They are still in development, have not been established as reliable screening
tests, and have not been endorsed 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 5 years if it’s negative.
7. What else can I do to prevent the
development of colorectal cancer?
- 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 sigmoidoscopic exam
every 3 to 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; non-hereditary
polyposis; colorectal 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 must 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 high fiber (vegetables) and low 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.
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