Treatment of Early-Stage Colorectal Cancer is associated with excellent outcome achieving cure in many cases. However, many colorectal cancers are diagnosed at a later stage.

Increasing awareness and promoting Screening programs have been shown to increase early-stage detection. Screening is also to detect and remove pre-cancerous polyps which if removed, may prevent cancer from developing.

Screening for Colorectal Cancer is directed at:

1. Early detection of cancer
2. The detection of polyps - which are usually without symptoms
3. Removal of pre-cancerous polyps which may then reduce the chance of one developing colorectal cancer

‘Screening’ means to subject an Individual who has no symptoms or complaints for a test to look for or rule-out a disease or early signs of the disease. An individual who has symptoms and signs undergoes ‘investigation’ (not screening) of a disease.

General population screening for Colorectal Cancer is recommended in most countries where healthcare systems are well developed. While the cost-benefit of population screening is contentious in less developed economies, the Screening of Increased-Risk populations is undoubtedly worthwhile and recommended.

Colonoscopy Screening is especially recommended for people who belong to ‘Increased-Risk’ Groups. This includes individuals with a family history of Colorectal cancer (especially first-degree relatives), a personal or family history of polyps.

There are a few tests available for screening of Colorectal Cancer, of varying degrees of ease, complexity, and accuracy.

Stool tests

1. Fecal Occult Blood Test (FOBT) or Fecal Immunochemical Stool Test (FIT). These tests entail taking stool samples and testing for traces of blood/blood protein in the stool.
2. False Positive or False negative test results may occur. The FIT is more specific for detecting occult bleeding from the Colon and does not need any dietary restrictions before the test.
3. There are some newer tests that detect DNA in the stool which are more accurate and more expensive than FOBT or FIT but are not widely available yet.
4. Stool tests are not as accurate as CT Colonography or Colonoscopy.
5. Stool Tests are to be used ONLY for screening and should not be used to investigate an individual with signs or symptoms.

XRays/Scans

1. CT Colonography is a CT scan of the Colon. This can detect polyps and cancers but is not as accurate as a Colonoscopy, especially for small lesions or ‘flat’ lesions. If abnormalities are detected, a Colonoscopy would likely still be required.
2. Barium enema is an older type of X Ray and is no longer recommended for screening

Blood Tests

1. Blood tests for Cancer Markers like Carcino-Embryonic Antigen (CEA) or CA 19-9 are NOT recommended as a method for screening for Colorectal Cancer
2. However, if the cancer markers are elevated in an asymptomatic patient, possible sources like, but not limited to, the Colon should be investigated

Colonoscopy

1. Colonoscopy is likely the most accurate method for screening for Polyps and Colorectal Cancer
2. Recommendations for commencing ‘Screening Colonoscopy” is at 50 years old for ‘average risk’ individuals and 40 years old for ‘increased risk’ individuals or 10 years earlier than the age of the affected first degree relative with Colorectal Cancer.
3. There is, presently, a move to advise commencement of Colonoscopy Screening at an earlier age (45 years old) for average risk individuals
4. Although colonoscopy is a more involved procedure with a higher cost, it has the added advantage that it can both detect and remove polyps that are seen during the procedure. It is hypothesized that removing polyps before it has the opportunity and time to turn cancerous, may reduce the chance of one developing colorectal cancer.
5. The time interval between colonoscopies will depend on various factors like whether polyps are seen and removed, type, size, number of polyps, family history, adequacy of bowel preparation
6. Colonoscopy Screening, although not without risk, is determined to be safe enough to advocate for population screening where the potential benefits far outweigh the very low risks

Risk of ‘Missed Lesions’

Although the colonoscopy is likely the ‘best test’ for screening and diagnosing colon lesions, there is still a chance of missing lesions. This rate is about 6%, no matter how diligent the endoscopist conducting the procedure is. Many factors can reduce the accuracy of the scope including inadequate cleanliness of the bowel, diverticular disease, lesions in the ascending and sigmoid colon, lesions at the flexures, inadequate sedation, long loopy colons, flat lesions, lesions behind folds and inadequate distension of the colon, among others. Careful withdrawal and hence, careful inspection of the colon and a minimum cecal withdrawal time of at least 6 minutes is recommended.

Patients who continue to have suspicious symptoms even after a recent ‘normal’ colonoscopy are advised to consult their doctors and, sometimes, a repeat scope may be required in persisting, unexplained symptoms.