The term “screening” refers to doing tests to look for evidence of a particular disease in a person who has no symptoms. Examples include breast mammograms, skin checks and PAP smears.
Colon (also known as bowel or colorectal) cancer is ideal for screening for a number of reasons.
- It is a very common cancer, affecting 1 in 18 males and 1 in 22 females in Australia.
- It is curable, by surgery, if found at an early stage. Symptoms of colon cancer often develop only in later stages of disease.
- Most (probably more than 95%) colon cancer begins as a benign polyp which is likely to cause no symptoms. These polyps, which may turn into cancer, can be removed from the colon before cancer develops. This prevents cancer even developing.
Faecal occult blood test (FOBT)
Faecal occult blood tests look for traces of blood in stools, on the assumption that most colon cancers bleed. FOBT screening has been shown in a number of studies to significantly reduce mortality from colon cancer. It is a safe and simple test and can be done through your local doctor. It will not pick up all cancers because not all cancers bleed. It commonly produces a “false positive” result; ie a positive result in someone who does not have colon cancer. This is because there are many other benign and often trivial causes for bowel bleeding. FOBT is not good at picking up colonic polyps as most do not bleed.
If a person has a positive FOBT it is essential that he or she has a colonoscopy, even though most will not turn out to have cancer.
The Australian government currently recommends FOBT every 5 years, starting at age 50. However the studies showing that FOBT can reduce mortality from bowel cancer were in populations having FOBT every 1- 2 years.
Many western countries recommend colonoscopy as the best way to screen for colon cancer. Although no test is perfect, it is the most accurate method currently available for diagnosing colon cancer and is far more accurate than FOBT. However, its main advantage over FOBT is finding and removal of premalignant polyps at colonoscopy – it can prevent colon cancer.
Colonoscopy has been shown not just to reduce colon cancer mortality but also to reduce colon cancer incidence.
The downside of colonoscopy is that it has a small risk of serious complications, it requires an unpleasant bowel clean out, a short stay in hospital, a day off work… It is also a more expensive test for the community.
At what age should colon cancer screening start?
Colon cancer is uncommon in young people and it is generally recommended that screening begin at age 50. Screening may start earlier if there is a strong family history of bowel cancer, such as people with young relatives or multiple relatives affected.
Should I have FOBT or colonoscopy?
This should always be discussed with your doctor.
- Colonoscopy is more accurate for screening but FOBT is safer, easier and cheaper.
- Colonoscopy can prevent cancer, by polyp detection and removal. FOBT is less likely to detect polyps and therefore less likely to prevent cancer.
All people with a positive FOBT should be further investigated with a colonoscopy.
If you have colonic symptoms, you do not require colon cancer screening (which implies you have no symptoms). Rather, you should be investigated with a colonoscopy. FOBT is not the appropriate test if you have colonic symptoms.
Screening with a colonoscopy is preferred in a person with a strong family history of colon cancer.