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HOME | What is Colon Cancer?
Colon cancer is an abnormal (or malignant) growth arising from
the inner lining (mucosa) of the large bowel. Like a person with many
names, colon cancer can also be called large bowel cancer or
colorectal cancer. If left untreated, colon cancer can grow larger and
spreads through the wall to the outer surface of the bowel. It may also
spread via the blood stream or lymphatic system to other parts of the
body. Secondary growths may develop in distant organs, such as the
liver or lung.
Colon cancer is one of the commonest cancers affecting both man and
women. In Hong Kong, it is the second commonest cancer and the third
commonest cause of cancer death. Every year, more than 3,000 Hong
Kong people are found to have colon cancer. People over 40 years of
age are more likely to develop this cancer, and the risk increases as we
grow older. The average age of colon cancer sufferers in Hong Kong is
60 years old.
The large bowel consists of two main parts: the colon and the rectum.
Colon is a muscular tube forming the last two metres of the body’s
digestive system. Rectum is the short tube leading down from the end of
the colon to the back passage.
What Causes Colon Cancer?
We don’t know for certain what causes colon cancer. Majority (80%) of
colon cancers are related to environmental causes particularly our diet.
Some food may help protect us from colon cancer, while others may
help it develop. There is growing evidence that a high fat and low fibre
diet is related to colon cancer. On the other hand, eating plenty of fruits,
vegetables and produce high in fibre (such as cereals, brown rice/
bread) may help prevent colon cancer.
About 20% of colon cancer are related to heredity. People with close
relative(s) (parents, brothers, sisters or children) having colon cancer
are more likely to develop it. The level of risk depends on the number of
close relatives with colon cancer and their age of developing cancer.
What are the Symptoms of Colon Cancer?
Colon cancer may develop the following symptoms :
· Blood or mucus (or both) in the bowel movements
· Unexplained changes in bowel habits lasting more than two weeks,
such as constipation or diarrhoea or both
· Persistent “colicky pain” in the abdomen
· Tiredness or paleness from anaemia
Sometimes, symptoms appear only after the colon cancer has spread.
On the other hand, in many cases these symptoms do not mean cancer,
but tests may be needed to make sure. The older you are, the more
likely that the symptoms could mean cancer.
What are Polyps?
Polyps are mushroom-shaped growths on the inner lining of the large
bowel. Although they are non-cancerous, one type of polyp called
adenoma is the precursor of colon cancer. If untreated, some adenoma
will grow bigger and become cancerous in a number of years.
Polyposis is a hereditary condition in which an individual develops
hundreds of polyps in the large bowel. For more information, please go
to the section on FAP.
Who is Most At-Risk?
For an average person, the risk of colon cancer increases with age from
50 years onwards. Individuals having close relatives with colon cancer
are at-risk. The risk increases with increasing number of affected close
relatives. A person with a history of large or numerous colonic adenoma
or a history of extensive ulcerative colitis for more than ten years are
also at risk of colon cancer.
Those most at-risk are individuals with hereditary colon cancer
syndromes caused by abnormal change (mutation) of known genes.
These include: polyposis syndrome which is a rare but easily
recognizable condition; non-polyposis syndrome which has no easily
recognizable features except a strong family history of colon cancer.
Genetic testing is helpful in pinpointing these conditions.
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