Colorectal cancer (CRC) is the second most common cancer in men and the third most common cancer in women.
Ontario has a colorectal cancer screening program called ColonCancerCheck (CCC). The program recommends that those between the ages of 50 and 74 with no personal or family history of CRC be screened using the fecal occult blood test (FOBT) every two years. For individuals at increased risk due to one or more first degree relative(s) with CRC, it recommends colonoscopy starting at the age of 50, or 10 years earlier than the age at which their relative was diagnosed, whichever comes first.
The overall participation to CRC screening in Ontario remains low. In 2012, 57.8% of at-risk Ontarians were up-to-date with CRC screening (FOBT, colonoscopy and flexible sigmoidoscopy) – 58.7% in the Champlain LHIN.
Different screening modalities
There is strong evidence (level one) that screening with FOBT every 1-2 years reduces CRC mortality by 16%. In 2011-2012, 29.9% of eligible Ontarians completed at least one FOBT during the two-year period; the Champlain LHIN had the highest rate of FOBT screening (35.5%).
The FOBT is relatively simple, cheap and accessible. However, the FOBT has been criticized for its low sensitivity. This limitation has prompted many CRC screening programs in Canada and in Europe to use the fecal immunochemical test (FIT) as entry-level CRC screening test instead of the FOBT.
The FIT is an immunoassay that detects the presence of human blood in stools. It can detect much lower amounts of blood than the FOBT does, it is not affected by dietary changes, and it is more specific for colonic sources of blood.
In 2010, Cancer Care Ontario (CCO) and Program in Evidence-Based Care (PEBC) formed the FIT Guidelines Expert Panel to review and evaluate the evidence for FIT CRC screening. The panel concluded that FIT has a greater sensitivity for detecting cancer, a much greater sensitivity for detecting advanced adenoma, and that it achieves higher screening participation rates.
CCO is working with the Ministry of Health and Long-Term Care to develop a plan to fund and implement FIT in the CCC program as the recommended screening test for those at average-risk of developing CRC.
There is also strong evidence to support the use of flexible sigmoidoscopy (FS) in persons at average risk for CRC.
FS every 5 years or once in a lifetime has been shown to decrease CRC incidence by about 20% and CRC mortality by 25%. The anticipated harms associated with FS (including follow-up colonoscopy for those with positive tests) are small and are outweighed by the benefits. CCO has piloted the Registered Nurse Flexible Sigmoidoscopy (RNFS) program, with sites in several regions, including the Montfort Hospital and The Ottawa Hospital.
Colonoscopy remains the gold standard intervention for follow- up of individuals with abnormal screening tests. However, there are no randomized controlled trials of the effectiveness and safety of colonoscopy for average risk screening.
CT colonography use for population-based screening has not been studied, although a Canadian economic evaluation revealed its use, for population-based screening, would be more resource intensive than an endoscopy-based or FOBT- based screening program. By comparison with colonoscopy, it is as good at detecting polyps that are greater than 1 cm in size, but less sensitive for smaller polyps.
Serologic blood tests for CRC screening, such as the Cologic test, are being promoted by some laboratories. The scientific evidence is insufficient to recommend or endorse their use, and as such, CCO is not able to offer a recommendation on follow-up of abnormal results.
In summary, CRC is one of the leading causes of cancer- related morbidity and mortality in Ontario. Screening can effectively reduce the risk of these harms. Although there are multiple tests available for CRC screening, there is strong evidence in support of only a few such tests in the context of an organized, population-based, screening program. CCC currently recommends that average-risk individuals aged 50 to74 be screened with FOBT every 2 years.
Article written by: Dr. Catherine Dubé, Provincial Clinical Lead, ColonCancerCheck