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How does colorectal cancer develop?
All of the body’s cells normally divide, grow, and die to keep the body
healthy and functioning properly. Sometimes this process goes out of control,
and cells keep dividing and growing even when the cells are supposed to die.
Colorectal cancer develops when the cells lining the colon and rectum are
affected by uncontrolled growth in the cells, and when older cells do not die.
Colorectal cancer is common in both men and women, and is curable if found
early. Fortunately, most colorectal cancers begin as small polyps. Polyps
usually grow slowly and do not cause symptoms until they become large or
cancerous. That is why it is important to screen for colorectal polyps and
cancer before symptoms develop.
When should screening begin?
Screening for colorectal cancer should begin at the age of 50, when the risk
for developing colorectal polyps and cancer increases. However, if you have a
personal or a family history of colorectal polyps or cancer, screening should
begin at age 40 or younger in some circumstances.
What is involved in screening for colorectal cancer?
Several tests are used to screen for colorectal cancer. The following is a list
of the most common screening tests, as well when they should be done. Although
colonoscopy is recommended, other options are available.
- Colonoscopy— Colonoscopy is the best procedure to check for
colorectal polyps and cancer. It allows polyps to be removed during the
exam. Colonoscopy is an outpatient procedure in which a physician uses a
long, flexible scope to view the rectum and entire colon. This 15- to
30-minute exam requires a bowel preparation and a light sedative. It is
usually repeated once every 10 years starting at age 50, unless polyps are
found.
- Fecal occult blood test (FOBT)— This is the least accurate
colorectal cancer screening test. It is done at home and tests for blood in
the stool, which may be caused by polyps or cancer. If this test is the one
chosen, it should be done yearly after age 50. If blood is detected on any
specimen, a colonoscopy is needed.
- Flexible sigmoidoscopy— This is a 10-minute outpatient
procedure in which the inside of the lower large intestine (called the
recto-sigmoid) is examined using a special thin scope. This test should be
done every 5 years after age 50 and should be done in a program of FOBT.
Or
- Double contrast barium enema— This is an X-ray examination of
the colon in which barium is given as an enema (through the rectum). Air is
then blown into the colon to make the barium spread over the lining of the
colon, producing an outline of the colon on X-ray. Barium enema is not the
most accurate method and should not be the procedure of choice for colorectal
cancer screening.
New techniques
One of the newest methods to screen for colorectal polyps and cancer is a
stool test that detects abnormal DNA in stool. While no one recommends that this test
replace colonoscopy, it appears to be much more accurate than FOBT:
- Fecal DNA test—The fecal DNA test works by detecting genetic
mutations in the stool. Genetic material, called DNA, is present in every
cell of the body, including the cells lining the colon. Normal colon cells
and their genetic material are passed into/in bowel movements every day.
When a colorectal polyp or cancer develops, abnormalities (or mutations)
occur in the genetic material of the colon’s cells. The mutations present
in the polyp or cancer can be detected by laboratory analysis of the stool.
What if I have a family history of colorectal cancer?
For people with a family history of colorectal cancer, the screening
recommendations are adjusted slightly to include the following:
- Begin screening at an age approximately 10 years earlier than
the age at which the youngest person in your family was diagnosed with colorectal polyps or
cancer. For example, if the youngest person in your family was diagnosed
with colorectal cancer at age 48, you should begin screening at age 38
rather than 50.
- Because polyps frequently are found on the right side of the
colon, screening in patients with a family history should be done with a
full colonoscopy.
What if I have polyps?
There are a variety of colorectal polyps, but cancer is thought only to arise
from adenomas. The follow-up check for patients with pre-cancerous polyps,
called adenomas, includes the following:
- Repeat the colonoscopy in 3 to 5 years
- Repeat the colonoscopy in 10 years if the second exam shows no new
polyps
What are the signs of colorectal cancer?
Even if you do not have a family history of colorectal cancer, tell your
doctor if you have any of the signs of colorectal cancer, no matter what your
age. Common signs of colorectal cancer include the following:
- Change in bowel habits (constipation or diarrhea)
- Blood on or in the stool that is either bright or very dark
- Unusual abdominal or gas pains
- Very narrow stool
- A feeling that the bowel has not emptied completely after
passing stool
- Unexplained weight loss
- Fatigue
- Vomiting
This information is not intended to replace the medical advice of your doctor
or health care provider. Please consult your health care provider for advice
about a specific medical condition.
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