Screening for Colorectal Cancer

Dear Dr. B: What is the best screening tool for early detection of colorectal polyps and cancer? What are the guidelines for screening?

Answer: This subject is gaining more importance each day. In the month of March I was at Peter Lougheed Centre, Calgary to attend a seminar on Update on Colon Cancer and Endoscopy organized by the University of Calgary’s Division of Gastroenterology. One of the topics for discussion was on colon cancer screening guidelines.

Colorectal cancer is the fourth most common cancer. It is the second leading cause of cancer death in Canada. In 2004, 19,100 new cases of colorectal cancers were diagnosed in Canada and 8300 deaths were reported.

Screening for colorectal cancer is recommended to pick up polyps and cancer at an early stage when they can be treated effectively. Currently we do not know what the best test is for screening purposes. A variety of tests are now available, each with advantages and disadvantages.

Every individual is at risk of developing colorectal cancer. The average lifetime risk of developing colorectal cancer is six per cent. If you have any of the following risk factors then the risk increases:
-Family history of colorectal cancer or polyps
-Ulcerative colitis or Crohn’s colitis
-Presence of polyps or previous history of colorectal cancer

What is the approach to an individual with average risk of colorectal cancer?

For asymptomatic men and women who are 50 years or older with no family history of colorectal cancer are considered to have average risk and the following options are available for screening:
-Fecal occult blood tests yearly or bi-annually
-Flexible sigmoidoscopy every five years
-Fecal occult blood tests plus flexible sigmoidoscopy every five years
-Barium enema every five years
-Colonoscopy every 10 years

What is the approach to an individual with above average risk of colorectal cancer?

For asymptomatic men and women age 50 or over with a positive family history of colorectal cancer the lifetime risk of developing colorectal cancer is anywhere from 15 per cent to 80 per cent depending on how many first degree relatives had colon cancer and at what age.
-If two or more first degree relatives have had colon cancer and if one of them is under the age of 60 then colonoscopy is advised at the age of 40 or 10 years earlier than the affected first degree relative and then every five years
-If only one first degree relative has colorectal cancer and is 60 years old or older then the individual is considered to have average risk and the screening starts at age 40
-If there is a hereditary history of polyps then genetic testing and colonoscopy is advised.

Fecal occult blood tests are done by patients and stool samples are taken to a lab to detect traces of blood not visible to naked eye. If positive then the patient needs a colonoscopy in the hospital. If negative then the test is repeated yearly or every two years. If done annually death rate from colorectal cancer is reduced by 30 to 45 per cent. The test can be combined with a short scope (flexible sigmoidoscopy) which is an office procedure. We do flexible sigmoidoscopy in our office on a regular basis. This can be repeated every five years.

Barium enema and colonoscopy are done in the hospital. If abnormality is found on a barium enema then colonoscopy is required. If colonoscopy is normal then it should be repeated every ten years for an average risk person. If less than one centimeter adenomatous polyp is found then the scope should be repeated in five years. If the polyp is bigger than one centimeter then it should be repeated after three years.

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