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.
  • Colorectal cancer rates are increasing in Maori although still lower than non-Maori in NZ
  • 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

• 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 an alternative  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).
  • Most colonoscopists consider that this approach leads to loss of important information on future risk (for example 3 adenomas less than 10mm significantly increases the lifetime risk of CRC) and therefore there is a lost opportunity to lower the risk.
  • 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.
    
    
• If polyps are expected then colonoscopy is the appropriate test
• All follow-up examinations once polyps have been detected should be by colonoscopy

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.