Annually in France there are about 36 000 new cases of colorectal cancer. The average age of onset is 70 years.
This is a rare cancer before age 50 (less than 5%). Its incidence has increased significantly between 1970 and 1990, which is not only due to the aging population. This cancer is responsible for 16,000 deaths annually.
A majority of colorectal cancer (60-80% of cases) results from a malignant transformation of a preexisting lesion, the adenomatous polyp.
We can define three levels of risk for colorectal cancer:
– The medium risk corresponding to the general population or the cumulative risk of developing cancer is about 4%;
– High risk: 15 to 20% of sporadic colorectal cancers have a family history of colon cancer in the first degree.The risk appears to be doubled in case of 1st degree relatives reached, and multiplied by 4 if the index cancer occurred before the age of 45 or if both parents are met;Another high-risk group is the patient with ulcerative colitis or Crohn’s disease;
– The very high risk corresponds to 2 situations: familial adenomatous polyposis (less than 1% of colorectal cancers) and HNPCC or Lynch syndrome (Human Non Polyposis Colic Cancer).
Familial adenomatous polyposis is a genetic disease linked to a mutation on a gene on chromosome 5, autosomal dominant.
When a family is known carrier of this mutation, it can be searched systematically in all of the siblings.
Lynch syndrome or familial colon cancer syndrome is responsible for 1 to 5% of cases of colorectal cancer in France: it is defined by the following three clinical criteria (Amsterdam criteria):
– Three patients with colorectal cancer, one of them being united to the other two by a first degree of relationship;
– Two generations are concerned;
– By one of the patients diagnosed with colorectal cancer was increased before the age of 50 years.
There may be also a higher risk of endometrial cancer, ovarian cancer, other cancers of the digestive and urinary urinary tract.
PREVENTION AND SCREENING:
Role of food:
Excess meat, fat and calorie overload are reported in many studies. The protective effect of vegetables and a high fiber diet is often mentioned. It seems that physical activity has a rather protective action.
The result of these studies, rather vague, does not establish very specific recommendations outside of general hygiene rules are common sense.
Preventive role of aspirin and nonsteroidal anti-inflammatory drugs:
The protective effect of aspirin and nonsteroidal anti-inflammatory drugs has been confirmed in several studies.However, the level of evidence is still insufficient to recommend the generalization of prevention as well as aspirin NSAIDs, and especially as the potential side effects are important.
In individuals at average risk:
Because of the number of people involved, the ideal screening test should be of low cost, innocuous, high sensitivity and specificity.
Colonoscopy, due to its cost, its risk can not be considered as a mass screening.
The Hemoccult test which was proposed to the general population among people aged 50 to 74 years has shown, when it was repeated every two years, followed by a colonoscopy if positive (2% of tests) that could reduce colorectal cancer mortality by 15 to 18%, 8-10 years after its establishment, provided that at least half of the population has agreed to perform the test. This test can detect about 50% of cancers and 20% of adenomas larger than 20 mm. The Hemoccult can be considered only in the context of a mass screening and constitutes neither an individual screening test, its sensitivity is too low.
In high risk:
It is advisable in this case a screening colonoscopy at all related to Ist degree of a patient with an incident colorectal cancer before age 60 years. This recommendation also applies if both parents are in the first degree with colorectal cancer, regardless of age and diagnosis.
Colonoscopy should be done in this case from 45 years or 5 years before the age of diagnosis of the index case.
In normal review, subsequent monitoring is a colonoscopy every 5 years.
In very high risk:
In subjects belonging to a carrier gene family of familial adenomatous polyposis is best genetic testing when it is possible: in the absence of the mutation, the risk of the subject concerned joins that of the general population.
In case of positive mutation or if the mutation is unknown should be offered from puberty colonoscopy and / or sigmoidoscopy every year until the age of 40 years.
If colon cancer family syndrome fulfilling the Amsterdam criteria, guidelines are complete colonoscopy every two years from the age of 25 years or 5 years before the age of diagnosis of the earliest cases in family. It is also recommended a complete gynecological examination from the age of 30 years.
If resection adenoma during colonoscopy, the risk of relapse to 4 years is estimated at 50%. However, the risk of malignant adenomas constitute a small proportion among the recurrent adenomas. Considering that adenomas are at risk (1) – the large adenomas greater than 1 cm; (2) – villous adenomas; (3) – adenomas with severe dysplasia or adenocarcinoma seat already in situ.
A predictive relapse adenomas is their number during the colonoscopy.
It is well established by numerous studies that the systematic removal of adenomas by colonoscopy allows a very important and significant decrease in colon cancer 10 years later.
There is, against the risk of missing a neoplastic lesion demonstrated by the development of cancer in the two years following the completion of a full colonoscopy as normal.
The risk is estimated to be between 2 and 5% in the various international studies: the quality of colonoscopy should be another element of decision in the rhythm of surveillance; incomplete colonoscopy or of poor quality due to poor preparation should not be considered sufficient security.
Hyperplastic polyps do not present a risk of degeneration except in exceptional cases or if they are large and therefore should not determine special surveillance.
Serrated adenomas, combining within the same polyp hyperplastic and adenomatous two structures by against the risk of degeneration and should be monitored.
According to current recommendations, a complete colonoscopy should be performed routinely three years after the first examination in cases of ill high risk of recurrence: Multiple adenomas greater than 1 cm in size, villous component. After a negative control, further tests must be carried out every 5 years.
In patients who underwent removal of adenomatous polyps low risk (less than two adenomas less than 1 cm), we can propose a control at 5 years is a lack of supervision according to the authors, by age of the patient.
In case of personal history:
If colorectal cancer curatively treated personal history, a colonoscopy should be considered within six months after surgery if the initial colonoscopy was incomplete (impassable stenosis) or if the cancer has revealed by an occlusion. Subsequently, a colonoscopy every three years is simply necessary, then every 5 years if normal.
The strategy for screening average-risk subjects currently remains the main focus of the debate and the subject of many evaluations in the international literature. In France, the widespread use of the Hemoccult test is in progress with the necessary and active collaboration of physicians, since the participation of at least half of the population of 50 to 74 is imperative, renewed every 2 years, the effectiveness of this campaign is significant. In other countries, various strategies are being considered, including the practice of systematic sigmoidoscopy every 5 or 10 years from 50 years, a full colonoscopy every 10 years or once in life to 60 years. The cost-effectiveness of these measures, compared to the strategies already in place for other conditions (including breast cancer) is essential to assess to validate either.
To these already proven screening technologies will add new approaches not yet validated soon as virtual colonoscopy (CT scan or MRI) or search by gene amplification in feces of mutations present in tumor cells that are eliminated in feces. These techniques, the sensitivity, specificity and cost are still poorly understood may alter the strategies developed in this chapter.