Colon Cancer Screening And Surveillance
Medical Author: Dennis Lee, MD
Medical Editor: Jay W. Marks, MD
Introduction to colon cancer screening and
surveillance
The colon, also
known as the large intestine or large bowel, constitutes the last part of the digestive tract. The colon is a long, muscular tube that receives undigested food from the small intestine. It removes water from the undigested food, stores it and then finally eliminates it from the body through bowel movements.
The rectum is the last part of the colon adjacent to the
anus.
Cancer of the colon and rectum (colorectal cancer)
is a
malignant tumor arising from the inner wall of the large intestine. These malignant tumors invade nearby tissue and spread to other parts of the
body. Benign tumors
of the colon are called polyps. Benign polyps do not invade
nearby
tissue or spread to other parts of the body like malignant tumors do. Benign polyps can
be removed
easily during colonoscopy and are not life threatening.
However, if
benign polyps are not removed from the large intestine, they
can become
malignant (cancerous) over time. In fact, most of the cancers
of the large
intestine are believed to have evolved from benign
polyps that are pre-cancerous, that is, they are benign at first but later become cancerous.
Cancer of the colon and rectum invades and damages adjacent tissues
and
organs. Cancer cells also can break away and spread to other
parts of the
body (such as the liver and lung) where new tumors grow. The sprocess
whereby colon
cancer preads to distant organs is called metastasis, and the new tumors are called metastases.
Once metastasis has occurred in colorectal cancer, a complete
cure of the
cancer is unlikely.
Colorectal cancer is both preventable and curable. Colorectal
cancer is
prevented by removing precancerous colon polyps
. It is cured if it is found early
and is surgically
removed before it spreads to other parts of the
body. The National
Polyp Study showed in its surveillance program that individuals who
had
their polyps removed experienced a 90% reduction in the incidence of
colorectal cancer.
The few patients in the study who did develop colorectal cancer had their
cancer discovered at
early, surgically or endoscopically curable stages. Since most colon polyps
and
early cancers are silent (produce no symptoms), it is important to do screening and surveillance for colon cancer
in patients
without symptoms or signs of the polyps or cancers. Recommendations
for
cost-effective public screening and surveillance have been
promulgated and
endorsed by numerous societies including the American Cancer
Society, the
National Cancer Institute, American College of
Gastroenterology, American
Medical Association, American College of Physicians, etc.
Next: Screening recommendations for individuals with
average risk of colon cancer »
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