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Colon Cancer and polyps

Cancer of the colon. This started as a polyp but has become larger and more irregular - now with more rapid and uncontrolled growth

Colon Cancer (also known as Bowel Cancer)

What are the risk factors for getting colon cancer?

  • Colon cancer is common in western countries.
    • New Zealand has a high rate of colon cancer. Each year there are over 2500 new cases AND over 1100 deaths from colon cancer.
    • The lifetime risk of getting colon cancer is 1:18. It is the second most common cause of cancer death in men (after lung cancer) and the 3rd most common in women (after breast and lung cancer).
  • The rate of colon cancer is rapidly increasing in countries adopting a “western” lifestyle.
    • For example there has been a 4-5 fold increase in deaths from colon cancer in Japan and Korea.
    • Asian men and women living in New Zealand need to seriously consider the risk of colon cancer as well as the well known increased risk of gastric cancer.
  • The risk of getting colon cancer is
    • Higher for men.
    • Higher if there has been a previous examination of the colon showing polyps.
    • Higher with a family history of colon cancer.
    • Higher with a family history of polyps of the colon.
  • Cancer develop from polyps therefore any finding of a polyp in the past is a marker of increased risk of colon cancer.

Hereditary or genetic factors for polyps and colon cancer.

  • 20% of people diagnosed with colon cancer will have a family member who has been diagnosed with colon cancer.
    • If you have a 1st degree relative affected with colon cancer then you have an approximate 2-fold increase in lifetime risk colon cancer.
    • If you have two 1st degree relatives affected then there is a 3-fold increase in lifetime risk. i.e a 1:6 lifetime risk of colon cancer. Referral to a gastroenterologist and perhaps to a familial bowel cancer clinic is required.
    • A younger age at diagnosis of colon cancer in your relative (< 55 yrs) also increases the risk.
  • There are two more specific genetic or hereditary conditions giving a high risk of colon cancer.
    • Hereditary non-polyposis colorectal cancer (HNPCC).
    • Familial adenomatous polyposis (FAP). More special tests may be required to detect an abnormal gene in the family.
  • More information is available at the New Zealand Guidelines Group website.www.nzgg.org.nz

Diagnosis is by colonoscopy

  • Barium enema is now very uncommon. It is a much less accurate for the diagnosis of polyps. A colonoscopy will be required if a polyp is found on barium enema.
  • Early diagnosis is crucial. Bowel cancer is cured in the majority if diagnosed in time.
  • This means taking note of rectal bleeding, change in bowel habit and anaemia and seeing your doctor and than having specialist evaluation if required.

CT colonoscopy is a new technique for investigating the colon.

  • This needs to be compared to colonoscopy.
    • This procedure does require some radiation exposure. Therefore there is some risk if used for repeated examinations.
    • Bowel preparation still needs to be taken.
    • Air or CO2 is inflated into the colon. There is some discomfort from the air. There is a small risk of perforation of the bowel.
    • There is less accuracy for detecting smaller polyps (less than 1cms).
    • Colonoscopy will still be required to remove the polyps that are detected - therefore there is a double procedure for about 25% of people.
    • CT colonoscopy has yet to find its place in investigation of bowel symptoms or as a screening tool. The debate requires more evidence. The technique is still developing but not yet accepted as a screening tool for colon cancer.

Treatment for Colon Cancer


The main treatment for colon cancer is surgical.

  • A segment of the large bowel is removed - usually about 1/3rd - and joined together again at the same operation
  • It is common now for the operation laparoscopically assisted - leaving only a small incision (required to remove the segment of bowel)
  • Chemotherapy or radiotherapy is given for more advanced disease to reduce the risk of recurrence.
  • These additional treatments are more commonly given for rectal cancer.
  • The majority of cancers of the rectum can now be removed without requiring a colostomy bag.
  • A colostomy will be required if the anal sphincter has been involved by cancer.
  • Your surgeon will discuss follow-up with CT/colonoscopy. It is usual to continue with surveillance colonoscopy 3-5 yearly.

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