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  • The large bowel is a muscular tube about 1.5 meters long. It is divided into two parts called the colon and the rectum (see adjacent diagram).
  • The large bowel is the last part of our digestive system. Unlike the small bowel which is responsible for absorption of digested nutrient, the role of the colon is to remove fluid from the liquid waste remaining after digestion. The rectum, the last 15 cm of our digestive tract, is a holding area for stool, the final form of this waste.
  • Bowel cancer (also called large bowel cancer, or colorectal cancer), is a malignant growth arising from the inner lining (the mucosa) of the large bowel (i.e. colon or rectum).
  • If left untreated, large bowel cancer can grow larger and spread through the wall to the outer surface of the bowel. It may also spread via the blood stream or the lymphatic system to other parts of the body. Spreads (or secondary growths) may develop in distant organs, such as the liver and the lung.
  • Colorectal cancer is one of the commonest cancers affecting both man and woman. In Hong Kong, colorectal cancer is the commonest cancer and the second cancer-killer. Every year, more than 4,900 Hong Kong people are found to have large bowel cancer. People over 50 years of age are more likely to develop this cancer, and the risk increases as we grow older. The average age of large bowel cancer in Hong Kong is 70 years old.
  • Moreover, in recent years, there has been a gradual increase in incidence of large bowel cancer in Hong Kong.

  • We don’t know for certain what causes bowel cancer. Majority (80%) of bowel cancer are related to environmental causes.
  • In its latest report, the World Cancer Research Fund (WCRF) concluded that there are convincing scientific evidence for the following environmental factors to be associated with bowel cancer risks.
    1. Convincingly decrease bowel cancer risk – physical activity, food containing dietary fibres;
    2. Convincingly increase bowel cancer risk – red meat, processed meat, alcoholic drinks (men), body fatness, abdominal fatness and adult attained height.
  • Certainly, our body-build, physical activity level, dietary and drinking habits have significant impact on our bowel cancer risk.
  • About 20% of bowel cancers are related to heredity. People with close relatives (parents, siblings or children) having bowel cancer are more likely to develop it. The level of risk depends on the number of close relatives with bowel cancer and their age of developing cancer.
  • (Ref: http://www.wcrf.org/sites/default/files/Colorectal-Cancer-2011-Report.pdf)
  • Bowel cancer may develop the following symptoms:

    1. Blood or mucus (or both) in the bowel movements;

    2. Unexplained changes in bowel habit lasting more than two weeks, such as constipation or diarrhoea or both;

    3. Persistent “colicky pain” in the abdomen;

    4. Tiredness or paleness from anaemia.

  • Sometimes, symptoms may appear only after the cancer has spread. However, in many cases, the above mentioned symptoms do not mean cancer; but tests may be needed to make sure. The older you are, the more likely that these symptoms could mean cancer.

  • Polyps are mushroom-shaped growths on the inner lining of the large bowel. There are many types of polyps and they are non-cancerous. However, one type of polyp called an adenoma or adenomatous polyp is the precursor of bowel cancer. If untreated, some adenoma will grow bigger and become cancerous a number of years later. Most adenoma, if found by colonoscopy, could be removed by a tiny instrument called a snare passing through the colonoscope. Removal of the adenoma will halt its transformation into cancer.
  • Polyposis is a hereditary condition in which an individual develops hundreds of polyps in the large bowel. The commonest type of polyposis is called familial adenomatous polyposis (FAP). For more information, please go to the section on FAP.
  • For an average person, the risk of bowel cancer increases with age from 50 years old onwards.
  • Individuals having close relatives (parents, siblings and children) with bowel cancer are at increased risk. The risk level increases with increasing number of affected close relatives.
  • A person with a previous history of large or numerous large bowel adenoma or a history of extensive inflammatory bowel disease, including ulcerative colitis and Crohn’s colitis, for more than ten years are also at risk of bowel cancer.
  • Those most at-risk are individuals with hereditary colorectal cancer syndromes caused by abnormal change (mutation) of known genes. These syndromes include: (1) polyposis syndrome which are rare but easily recognizable conditions; and (2) non-polyposis syndrome which has no easily recognizable features except a strong family history of bowel cancer. Genetic testing is helpful in pinpointing this latter condition.
  • Studies have shown that regular check-up (called screening) is the most effective way to prevent bowel cancer. Whether you are at-risk of bowel cancer or not, regular screening is your best bet against this very common cancer.
  • Even if you have no risk factor for bowel cancer, we recommend you to have regular bowel check-up from 50 years old onwards. The check-up options for an average risk person includes:
    1. Stool test of occult blood annually;
    2. Endoscopic examination of the lower part of the large bowel (called flexible sigmoidoscopy) every 5 years;
    3. Contrast examination of the large bowel (called barium enema) every 5 years;
    4. Endoscopic examination of the entire large bowel (called colonoscopy) every 10 years.
  • If you have a family history of bowel cancer, your check-up may have to start earlier, say from 40 years old onwards or even earlier. In your case, a colonoscopy (i.e. complete examination of the whole large bowel) is the best check-up option.
  • Apart from regular check-up, lifestyle changes can also reduce your bowel cancer risk.
  • Below are the ten personal recommendations from the World Cancer Research Fund regarding cancer prevention. Those highlighted with a √ relates to bowel cancer prevention.
    1. Be as lean as possible within the normal range of body weight – maintain body weight within the normal range from age 21; avoid weight gain and increases in waist circumference throughout adulthood (√);
    2. Be physically active as part of everyday life – be moderately physically active, equivalent to brisk walking for at least 30 minutes every day. As fitness improves, aim for 60 minutes or more of moderate, or for 30 minutes or more of vigorous, physical activity every day. Limit sedentary habits such as watching television (√);
    3. Limit consumption of energy-dense foods, avoid sugary drinks – consume energy-dense foods sparingly; avoid sugary drinks; consume “fast foods” sparingly, if at all (√);
    4. Eat mostly foods of plant origin – eat at least five portions/servings of a variety of non-starchy vegetables and of fruits every day (√);
    5. Limit intake of red meat and avoid processed meat – eat less than 500gm of red meat a week; very little if any to be processed meat (√);
    6. Limit alcoholic drinks – if alcoholic drinks are consumed, limit consumption to no more than two drinks a day for men and one drink a day for women (√);
    7. Limit consumption of salt, avoid mouldy cereals or pulses – avoid salt-preserved, salted, or salty foods; preserve foods without using salt. Limit consumption of processed foods with added salt to ensure an intake of less than 6gm salt (i.e. 2.6gm sodium) a day. Do not eat mouldy cereals or pulses;
    8. Aim to meet nutritional needs through diet alone – dietary supplements are not recommended for cancer prevention;
    9. Mothers to breastfeed; children to be breastfed – aim to breastfeed infants exclusively up to six months and continue with complementary feeding thereafter;
    10. For cancer survivors, the best is to follow the cancer prevention recommendations as mentioned above (√).