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.

What symptoms may suggest colon cancer?

• Cancers can present with rectal bleeding.
  • Most rectal bleeding (blood noted on the toilet paper or in the toilet bowl is due to haemorrhoids (piles) or to an anal fissure.
  • However for someone over 40 years with rectal bleeding the chance of finding a colon or rectal cancer is 5-10%.  Therefore rectal bleeding should never be ignored!
    
• A change in bowel habit or cramping lower abdominal pain may be from partial blockage.
  • There are many other reasons for variable bowel habit including irritable bowel syndrome and diverticular disease.
  • A change in bowel habit towards towards looser bowel motions is more important than a change to constipation - unless this change is accompanied by lower abdominal cramping pain
    
• Sometimes unexplained diarrhoea can be due to colon cancer.
  • Although there are many other possible reasons.
    
• Iron deficiency leading to anaemia(a low blood count) may be a sign of colon cancer.
  • This should never be simply treated with iron tablets without first having appropriate investigation.
  • This usually means combined gastroscopy and colonoscopy.
    
• There are still up to 20% of people that diagnosed after emergency admissions to hospital.
  • Usually with symptoms of obstruction or occasionally perforation.
  • Both conditions lead to severe abdominal pain.

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 or on CT colonography.
• 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.

Prevention of Colon Cancer

Diet

• There is an increased risk of polyps and cancer with
  • Higher intake of dairy foods and animal fat intake.
  • High intake of red meat.  There is a suggestion that the traditional kiwi BBQ may not be the best way of cooking meat as potential cancer-causing chemicals (carcinogens) are formed.
  • Diets low in fruit & vegetables  - therefore fruit and vegetables may have a protective effect.
  • Low dietary fibre.  This is the most well known dietary factor - but there is only modest evidence for high dietary fibre having a protective effect
    


• If you have had a polyp or colon cancer then these dietary suggestions are sensible.  However you cannot prevent more problems by diet alone.
• Regular checks by colonoscopy and removal of polyps as they form is the only definitely effective approach 
  • More specific dietary advice is not possible with the available evidence.

Medication / supplements

• Supplements such as Vitamin C & E, folate and calcium, vitamin D have been suggested as having a protective effect.
  • The evidence is conflicting and not strong enough to make any recommendations for taking regular supplements.
  • The data for vitamin C, and E and folate is largely negative - no protective effect.
  • Hormone replacement therapy decreases the risk of colon cancer. Unfortunately the increased risk of breast cancer outweighs this effect.


• One of the beneficial effects of low dose aspirin is a reduction in risk of colon cancer.
  • There is probably not enough benefit to recommend daily aspirin as a routine treatment but of course it is an additional benefit if aspirin has been already recommended for heart protection.
  • Anti-inflammatory drugs also have this effect.
  • Both anti-inflammatories and aspirin increase the risk of bleeding from the stomach.

Colonoscopy and removal of polyps

• Removal of polyps at the time of colonoscopy is highly protective against developing bowel cancer.
  • The problem is finding out which group of people are the “polyp formers” and therefore the group at risk of developing bowel cancer.
  • The acceptance of colonoscopy as a useful examination has increased.
  • More people are having an examination – therefore there is more chance of finding those with polyps and removing them – therefore removing the risk.
  • If you have had a polyp in the past then there needs to be ongoing checks.
    
  • The interval will vary from 3-5 years depending on the type and number of polyps found at a previous examination.
  • If you have a family history of bowel cancer then you should have a colonoscopy to assess your risk of developing bowel cancer.
    
  • This should be performed 10 years younger than the age of the youngest family member affected by bowel cancer.  Continued surveillance by colonoscopy every 5 years is recommended.

Population Screening

• This is an approach that is currently being debated by health systems in many countries.


• New Zealand has already accepted the idea of targeting those at higher risk of developing bowel cancer (mainly those with a family history.
• There will soon be a screening policy for people of average risk over the age of 55 years
  
  • Currently a pilot study of screening is being planned in NZ.
  • The current position of the Ministry of Health is discussed on the National Screening Unit website. www.moh.govt.nz/nationalscreeningunit
  • This is involve doing faeces tests checking for blood - then colonoscopy for those with a positive test
  • The faeces tests will posted out according to data for the polling register to those of eligible age.  The tests will be performed at home.  The test is specific for human blood and does not need any dietary restriction before taking the test
    


• The test can be requested by your GP.  This is a proven approach - called a faecal occult blood test
  • This has some inconvenience and some limitations.
    
  • There are false positive tests because of minor conditions such as hemorrhoids (piles).
    
  • Colon Cancer, if present, does not always bleed all of the time – therefore some cancers are missed.
  • However despite these problems a reduction in death rate from Colon Cancer can be demonstrated if screening using faecal occult tests is used.
  • If you have a positive test you should proceed to colonoscopy as there is a 1:10 chance that you will have cancer.
  Faecal blood tests are always going to be an indirect marker of a problem and the only way to be completely reassured is to have a colonoscopy.

Polyp in the colon

Another example of a colonic polyps - a resected specimen

Polyp

Polyps of the Colon

• These are small lumps or "outgrowths" on the lining of the bowel.

  • Small polyps are mainly hyperplastic. These polyps have very little risk of becoming cancer over time.
  • Larger polyps (over 1cms) are usually adenomas. These may be called tubular or villous depending on the appearance under the microscope.
    
  • Adenomas have a risk of becoming cancer over time.
  • Pathologists define polyps as "benign tumours". They will all have a degree of change called "dysplasia". This description is only relevant if the grading is severe dysplasia.
  • There is a new type of polyp called a sessile serrated polyp or adenoma.  This is been viewed in the same way as an adenoma  - i.e follow-up colonoscopy is required
    

• More facts about polyps

  • > 90% of colorectal cancers appear to arise from polyps. Polyps are found more frequently in populations with a high risk of colon cancer.
  • About 5% of polyps if left alone will eventually become malignant.
  • The transition from adenoma (polyp) to cancer takes at least 5-10 years.
  • 15 - 20% of people over the age 55 years have colonic polyps.
    
  • Polyps are more common in men than women.
  • The majority of polyps cause no symptoms. Only 5 % will bleed. Cramping abdominal pain caused by polyps is uncommon.
  • Polyps with a higher risk of becoming cancer are those with severe dysplasia (an appearance on microscopy), a villous appearance or size over >1cm in size.

Colonoscopic removal of Polyps

• Polyps can be safely removed at the time of a colonoscopy.
  • Small polyps are removed with diathermy (hot biopsy). A heating current is applied which destroys the polyp with heat energy.
  • Larger polyps need to be snared.  A circular wire is placed around the base of the polyp then cut off with diathermy current to control the bleeding.
  • These procedures are very safe. There is a small risk of bleeding - about 1in 500 procedures - the timing of bleeding is either in the first 24 hours after the procedure or 5-7 days after the procedure
  • Newer techniques mean that it is possible to remove nearly all polyps that are not already cancer - preventing the need for surgery
    


• Polyps are almost always benign but a small number can have a focus of cancer within the polyp.
  • These polyps may be removed at colonoscopy and no further treatment is required if there is complete excision shown under the microscope.
  • If there is some doubt about the completeness of excision then an operation to remove part of the colon will be required
• Complete removal of polyps significantly reduces the risk of developing colon cancer  - about a 80% reduction of risk (over following 10 years).  It most be noted that this risk reduction is not 100%.   The reduction is operator dependant  - it is important to have a high quality colonoscopy by an experienced endoscopist