Colon Cancer (cont.)
How can colon cancer be prevented?
Unfortunately, colon cancers can be well advanced before they are detected. The
most effective prevention of colon cancer is early detection and removal of
precancerous colon polyps before they turn cancerous. Even in cases where cancer
has already developed, early detection still significantly improves the chances
of a cure by surgically removing the cancer before the disease spreads to other
organs. Multiple world health organizations have suggested general screening
guidelines.
Digital rectal examination and stool occult blood testing
It is recommended that all individuals over the age of 40 have yearly digital
examinations of the rectum and their stool tested for hidden or "occult" blood.
During digital examination of the rectum, the doctor inserts a gloved finger
into the rectum to feel for abnormal growths. Stool samples can be obtained to
test for occult blood (see below). The prostate gland can be examined at the
same time.
An important screening test for colorectal cancers and polyps is the stool
occult blood test. Tumors of the colon and rectum tend to bleed slowly into the
stool. The small amount of blood mixed into the stool is usually not visible to
the naked eye. The commonly used stool occult blood tests rely on chemical color
conversions to detect microscopic amounts of blood. These tests are both
convenient and inexpensive. A small amount of stool sample is smeared on a
special card for occult blood testing. Usually, three consecutive stool cards
are collected. A person who tests positive for stool occult blood has a 30%
to 45% chance of having a colon polyp and a 3% to 5% chance of having a colon cancer. Colon cancers found under these
circumstances tend to be early and have a better long-term prognosis.
It is important to remember that having stool tested positive for occult blood
does not necessarily mean the person has colon cancer. Many other conditions can
cause occult blood in the stool. However, patients with a positive stool occult
blood should undergo further evaluations involving barium enema x-rays,
colonoscopies, and other tests to exclude colon cancer, and to explain the
source of the bleeding. It is also important to realize that stool which has
tested negative for occult blood does not mean the absence of colorectal cancer
or polyps. Even under ideal testing conditions, at least 20% of colon
cancers can be missed by stool occult blood screening. Many patients with colon
polyps are tested negative for stool occult blood. In patients suspected of
having colon tumors, and in those with high risk factors for developing
colorectal polyps and cancer, flexible sigmoidoscopies or screening
colonoscopies are performed even if the stool occult blood tests are negative.
Flexible sigmoidoscopy and
colonoscopy
Beginning at age 50, a flexible sigmoidoscopy screening tests is
recommended every three to five years. Flexible sigmoidoscopy is an exam of the rectum
and the lower colon using a viewing tube (a short version of colonoscopy).
Recent studies have shown that the use of screening flexible sigmoidoscopy can
reduce mortality from colon cancer. This is a result of the detection of polyps
or early cancers in people with no symptoms. If a polyp or cancer is found, a
complete colonoscopy
is recommended. The majority of colon polyps can be
completely removed by colonoscopy without open surgery. Recently doctors are
recommending screening colonoscopies instead of screening flexible
sigmoidoscopies for healthy individuals starting at ages 50-55. Please read the
Colon Cancer Screening article.
Patients with a high risk of developing colorectal cancer may undergo
colonoscopies starting at earlier ages than 50. For example, patients with
family history of colon cancer are recommended to start screening colonoscopies
at an age 10 years before the earliest colon caner diagnosed in a first-degree
relative, or five years earlier than the earliest precancerous colon polyp
discovered in a first-degree relative. Patients with hereditary colon cancer
syndromes such as FAP, AFAP, HNPCC, and MYH are recommended to begin
colonoscopies early. The recommendations differ depending on the genetic defect,
for example in FAP; colonoscopies may begin during teenage years to look for the
development of colon polyps. Patients with a prior history of polyps or colon
cancer may also undergo colonoscopies to exclude recurrence. Patients with a
long history (greater than 10 years) of chronic ulcerative colitis have an
increased risk of colon cancer, and should have regular colonoscopies to look
for precancerous changes in the colon lining.
Genetic counseling and testing
Blood tests are now available to test for FAP, AFAP, MYH, and HNPCC hereditary
colon cancer syndromes. Families with multiple members having colon cancers,
members with multiple colon polyps, members having cancers at young ages, and
having other cancers such as cancers of the ureters, uterus, duodenum, etc.,
should be referred for genetic counseling followed possibly by genetic testing.
Genetic testing without prior counseling is discouraged because of the extensive
family education that is involved and the complicated nature of interpreting the
test results.
The advantages of genetic counseling followed by genetic testing include: (1)
identifying family members at high risk of developing colon cancer to begin
colonoscopies early; (2) identifying high risk members so that screening may
begin to prevent other cancers such as ultrasound tests for uterine cancer,
urine examinations for ureter cancer, and upper endoscopies for stomach and
duodenal cancers; and (3) alleviating concern for members who test negative for the
hereditary genetic defects.
Diet and colon cancer to prevent colon cancer
People can change their eating habits by reducing fat intake and increasing
fiber (roughage) in their diet. Major
sources of fat are meat, eggs, dairy products, salad dressings, and oils used in
cooking. Fiber is the insoluble, nondigestible part of plant material present
in fruits, vegetables, and whole-grain breads and cereals. It is postulated that
high fiber in the diet leads to the creation of bulky stools which can rid the
intestines of potential carcinogens. In addition, fiber leads to the more rapid
transit of fecal material through the intestine, thus allowing less time for a
potential carcinogen to react with the intestinal lining. For additional
information, please read the Colon Cancer
Prevention article.
Next: What are the treatments and survival for colon cancer? »
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