What is colon cancer screening ?
Screening and early detection
Early detection of colorectal cancer and precancerous polyps is crucial because the earlier a cancer or polyp is detected, the greater the chances of a cure. In France, the strategy for screening and early detection is determined based on the risk level of a population or individual.
There are three levels of risk :
- Average risk : Men and women over 50 years old, asymptomatic (without symptoms suggesting the possibility of colorectal cancer).
- High risk : Individuals with a personal history of adenoma (benign tumor) or colorectal cancer, family history of colorectal cancer in first-degree relatives, or the presence of chronic inflammatory bowel disease.
- Very high risk : Patients with familial adenomatous polyposis or Lynch syndrome.
Average risk population
For the general population over 50 years old and at average risk, screening is organized in France.
EIn practice, it is recommended that all individuals in this group, male or female, undergo a stool blood test (Hemoccult™) every two years.
Unfortunately, participation rates in these screening campaigns remain disappointing despite the potential to reduce colorectal cancer mortality by 15 to 20%.
During the 2019-2020 period, the lowest participation rates were observed in Corsica (15%) and Paris (17%), while the highest were in Haut-Rhin (43%), Bas-Rhin (42%), and Maine-et-Loire (41%).
High-risk population
For individuals at high risk, individual screening is offered. In practice, this includes a consultation with a gastroenterologist and a screening colonoscopy or chromoendoscopy starting at age 45.
However, for those whose parent was diagnosed with colorectal cancer before age 55, screening colonoscopy is recommended starting at age 35. If the colonoscopy is normal, it should be repeated every 5 years. If abnormal (presence of high-risk polyps), it should be repeated every 2 to 3 years.
A recent study demonstrated that screening colonoscopy reduces the risk of colorectal cancer by 80% and has a similar effect on mortality due to this cancer (source: Nature Reviews Disease Primers).
Expert perspective
Colonoscopy is a medical imaging examination ( endoscopy ) that allows visualization of the inside of the rectum and colon. This procedure is performed by a gastroenterologist using an instrument called a colonoscope. The colonoscope consists of a thin, flexible tube that is 1.5 to 2 meters long, which is inserted through the anus.
Most colonoscopies are performed under general anesthesia, requiring a pre-procedure consultation with an anesthetist a few days before. The colonoscopy itself requires bowel preparation to ensure the intestine is clean and its walls are visible.
This involves following a special diet three days before the examination, which excludes fruits, vegetables, and fibers (as mentioned earlier). Meats and cold cuts should also be avoided. The day before the examination, a laxative is taken.
Nowadays, there are laxative solutions of a few milliliters that need to be mixed with about 2 liters of a chosen liquid without fibers or pulp (like mint water or iced tea). These laxative solutions are more pleasant to drink than the previous two-liter solutions. The procedure lasts about 30 minutes and is followed by a few hours of observation. The patient can then go home but should avoid driving due to the general anesthesia. Colonoscopy not only allows examination of the colon and rectum but also enables treatment of any lesions that can be removed during the procedure. These lesions can then be examined under a microscope by a pathologist to confirm or rule out their benign nature.
During the endoscopy, dyes can be used to better visualize certain lesions. This imaging procedure, similar to colonoscopy, is called chromoendoscopy.
Another medical imaging procedure, the virtual colonoscopy, allows a virtual view of the colon and rectum without the need to insert a colonoscope. However, it requires the same preparation as a colonoscopy. Additionally, if any abnormalities are detected, a colonoscopy must be performed afterward since the virtual colonoscopy does not allow for the removal of any polyps or adenomas.
Very high-risk population
For individuals at very high risk, individual screening is of course offered. Besides the consultation with a gastroenterologist, a genetic oncology consultation is also conducted to identify any mutations.
In these individuals, chromoendoscopy is preferred over regular colonoscopy without dye as it provides better detection of certain lesions (adenomas). The first examination is performed between ages 20 and 25 or 5 years before the earliest age of cancer diagnosis in the family. The frequency of monitoring with chromoendoscopy is tailored to each individual and can be as frequent as annually.
Interview with Professor Romain Coriat
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Article updated on Nov 14, 2024
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