Colorectal cancer is a common cancer: its incidence places it 3rd among the most common cancers, and it represents the 2nd cause of cancer mortality after lung cancer.
As the prognosis and chances of recovery depend on the stage of the disease at the time of diagnosis, screening is essential. What does it consist of, and who is affected?
[Un article de The Conversation écrit par Lucien Grados – Médecin spécialisé en gastroentérologie, chercheur associé au laboratoire Péritox (Périnatalité et risques toxiques) UMR-I 01, Université de Picardie Jules Verne (UPJV)]
What risk factors?
Each year, 51,636 new cases of colorectal cancer are recorded in France, and the disease is the cause of 21,218 annual deaths in our country. These statistics are taken from 2022 data from the GLOBOCAN registry, compiled by the International Agency for Research on Cancer (IARC – in English IARC, intergovernmental agency for cancer research, created in 1965 by the World Health Organization).
Before age 50, the age-standardized incidence rate is 7.9 cases per 100,000 people, while it reaches 201.2 and 283 per 100,000 after ages 60 and 70.
The main risk factors are age, the presence of a genetic predisposition syndrome (familial adenomatous polyposis, Lynch syndrome, etc.), chronic inflammatory bowel disease (IBD) including Crohn's disease and ulcerative colitis. hemorrhagic, a personal or family history of colonic adenoma or colorectal cancer, overweight, smoking, excessive alcohol consumption.
Diet also plays a major role and the main dietary risk factors (alcohol, cold meats, red meat, etc.) are well identified, as are the protective factors (foods rich in fiber, dairy products, physical activity, etc.).
As colorectal cancer is a slow-growing cancer, screening is essential to fight the disease. The prognosis of the disease depends in fact on its stage at the time of diagnosis, which is defined by the size of the tumor, its extension into the different layers of the wall of the colon, the presence or absence of invasion of the lymph nodes as well as damage to other parts of the body (presence or absence of metastases to the liver, peritoneum – the membrane that covers the abdominal cavity and viscera, lungs or other organs).
What symptoms should you worry about?
The main signs and symptoms are the presence after 50 years of digestive bleeding (rectorrhagia or melena – emission from the anus of black blood), a change in intestinal transit, weight loss associated with abdominal pain, a palpable abdominal mass, iron deficiency anemia (iron deficiency).
In younger subjects, it is the presence of alarm signs which will give rise to the indication: digestive bleeding with drop in hemoglobin level and/or iron deficiency, transit disorders or abdominal pain with alteration of the general condition, i.e. unusual intense fatigue, loss of appetite and/or weight loss, first-degree family history of colorectal cancer at a young age, persistent unexplained biological inflammatory syndrome, etc.
We often hear that everyone is affected by screening, but it is important to remember that only asymptomatic people are primarily concerned. Indeed, in the event of symptoms such as those mentioned above or signs suggestive of colorectal cancer, the patient is no longer concerned by screening: he must immediately benefit from a colonoscopy, and not from screening by stool test (this screening consists of looking for traces of blood in the stool that are invisible to the naked eye).
Colonoscopy is also used to screen asymptomatic people at high risk of colorectal cancer, due to family history or genetic predispositions, for example.
Why get tested?
Colorectal cancer develops in the majority of cases within 5 to 10 years from precancerous lesions: adenomas (or adenomatous polyps) and scalloped polyps.
Through the accumulation of mutations over time, these precancerous lesions will acquire the capacity for proliferation and dissemination, leading to the stage of invasive cancer called “adenocarcinoma”. Colonoscopy (examination carried out under general anesthesia after colonic preparation to explore the entire colon) makes it possible to detect possible precancerous lesions and remove them. This prevents the appearance of adenocarcinomas and therefore reduces the incidence of colorectal cancer.
The frequency of surveillance and the interval between two colonoscopies will depend on the size, number and type of polyps removed (codified in the 2022 recommendations of the French Society of Digestive Endoscopy – SFED).
The second objective of screening (after reducing the incidence of colorectal cancer by detecting pre-cancerous lesions) is the detection of cancers at an early stage. This makes it possible to drastically improve the prognosis of patients, because in 9 cases out of 10, a cure can be obtained by surgical operation, or even by a simple resection (ablation) carried out during the colonoscopy.
Unfortunately, at present, in France, around a third of colorectal cancers are diagnosed at a metastatic and unresectable stage.
Who is affected by screening?
The method of screening, the pace and the age of onset will depend on the individual risk of colorectal cancer. The population is considered to be divided into three categories:
- very high risk: these patients suffer from a genetic predisposition syndrome (familial adenomatous polyposis, Lynch syndrome, etc.). They must have a colonoscopy every 1 to 2 years from the age of 25, or sometimes earlier;
- high risk: these are either patients with a history of colonic adenoma or colorectal cancer – whether personal or first-degree family (parents, brother/sister and children). If the history is familial, these patients must perform a colonoscopy from the age of 50 (or 5 years before the age of the index case in the event of occurrence before age 55). This category also includes patients with chronic inflammatory bowel disease (IBD), with colonic involvement. They must benefit from colonoscopy with coloring (chromo-endoscopy) for screening every 1 to 5 years from 7 years of progression of the disease. The rate of screening will depend on the characteristics of the IBD and the history of colonic dysplasia lesions, or the association with primary sclerosing cholangitis;
- medium risk: any asymptomatic person aged 50 to 74. This last category represents the majority of the French population: the number of eligible people is estimated at 17.9 million people.
How is screening done when you are asymptomatic?
Screening in asymptomatic people of average risk requires carrying out a test for blood in the stool using a standardized test: the FIT test (immunological test). This test has replaced the Hémocult test (guaiac test) since 2015/2016 because it has demonstrated its superiority in terms of detection of advanced adenomas and invasive cancers. The test is carried out at home.
The test positivity rate is 3.6% and increases with age. Its sensitivity is approximately 70% and its specificity is 96 to 98% for the detection of adenoma or invasive cancer. Its positive predictive value (i.e. the probability of having a colonic lesion if the screening test is positive) is 28.4% for adenomas and 6.6% for invasive cancers.
Several options are possible to obtain it. Either a consultation with your GP or a specialist doctor, either in a community pharmacy, or by ordering online. A website helps guide patients through the procedures and even offers an explanatory video on carrying out the test.
In the event of a positive result (threshold at 30 µg of hemoglobin/g of stool), the patient is warned that he must consult a specialist to arrange an endoscopic assessment. In the event of a negative test, it must be renewed every 2 years.
Towards a lowering of the age of initial screening, and an extension of the duration?
In recent years, we have seen an increase in the number of colorectal cancers diagnosed before the age of 50. This age group now represents up to 10% of all colorectal cancers. They are often diagnosed at a more advanced stage and have a poorer prognosis.
Lowering the age at which screening begins to 45 or even 40 years would make it possible to detect these cancers earlier and considerably improve the prognosis of patients. In the United States, the screening age was lowered in 2018: since then, it starts at age 45.
It is also planned to extend the screening period up to 80 years, depending on the case. Indeed, the incidence of colorectal cancer increases with age and more than half of colorectal cancers are diagnosed after age 75. However, a systemic review of recent literature on the subject demonstrated that certain selected patients over 75 benefit from continuing screening until age 80.
However, the complication rate of colonoscopy under general anesthesia is also higher after age 75. This extension over time should therefore not be systematic, but rather be reserved for patients in good general condition, with few comorbidities and a high life expectancy.
To conclude, let us remember that one of the main problems in the fight against colorectal cancer is the low rate of participation in screening in France. In 2022-2023, only 34.2% of the eligible population used it, far from the 45% which constitutes the recommended European threshold.
Let us hope that the new methods of obtaining the test (online ordering and pharmacy), as well as the numerous communication campaigns (such as Blue Mars), which aim respectively to improve accessibility to the test and to better inform the populations concerned, will allow this percentage to increase in the years to come…
With an unwavering passion for local news, Christopher leads our editorial team with integrity and dedication. With over 20 years’ experience, he is the backbone of Wouldsayso, ensuring that we stay true to our mission to inform.
