What are the causes and risk factors for colon cancer ?

The risk factors for colorectal cancers are numerous. Some of these factors are directly related to an individual's constitution (constitutional factors), while others are related to the environment (environmental factors). It is the interaction between constitutional factors and environmental factors that leads to the development of polyps and then to the transformation of polyps into colorectal cancer.

1 - Genetic risk factors

Among the constitutional factors, heredity can play a role. 5 to 10% of patients with colorectal cancer have a genetic predisposition due to mutations that are passed down from one generation to another and are involved in the development of these cancers.

The most common form of hereditary colorectal cancer is due to Lynch syndrome, which accounts for 3 to 5% of colorectal cancers. It is a hereditary form without the presence of polyps.

The genes involved in Lynch syndrome are most often the MMR genes responsible for repairing mutations. When these genes are mutated or inactivated, DNA repair is no longer possible. Patients with Lynch syndrome have a higher risk of developing colorectal cancer, with the age of onset around 45 years. They also have an increased risk of endometrial (uterine), ovarian, stomach, small intestine, bile duct, or urinary tract cancer.

Another hereditary form of colorectal cancer is familial adenomatous polyposis (FAP), which accounts for about 1% of colorectal cancers. Patients with FAP will develop multiple polyps during the second decade of life, with the number increasing with age. This polyposis is due to a mutation in a tumor suppressor gene, the APC gene. The risk of cancer is about 50% by age 40 and nearly 100% by age 60. However, there are attenuated forms where the risk is lower.

Additionally, familial disposition is observed in 15 to 20% of patients. This can be due to a genetic predisposition, the lifestyle of family members, chance, or a combination of these factors. The risk of developing colorectal cancer during one's lifetime is doubled when a first-degree relative (father, mother, brother, sister, child) is diagnosed with colorectal cancer at the age of 50-70 years. The risk triples if the diagnosis is made in the first-degree relative before the age of 50.

A patient already treated for colorectal cancer has a higher risk of developing a second colorectal cancer. Women who have had breast, ovarian, or uterine cancer also have a slightly increased risk of developing colorectal cancer (source: arcagy.com).

Interview with Professor Romain Coriat

2 - Certain diseases

Chronic inflammatory bowel diseases (Crohn's disease and ulcerative colitis or UC) are also associated with an increased risk of colorectal cancer. The risk is higher for patients with UC. These inflammatory diseases account for only 0.4% of colorectal cancers, and this percentage is decreasing with improved management.

3 - Age

Age is another constitutional factor that increases the risk of colorectal cancer. Indeed, the number of new cases of colorectal cancer increases with age, and 90% of patients are over 50 years old.

4 - Environnemental factors

Besides these constitutional factors, several environmental factors related to lifestyle increase the risk of colorectal cancer. This includes smoking, alcohol, diet, being overweight, and lack of physical exercise.

Here are some pratical tips :

Have a diet rich in fiber, fruits, and vegetables

Legumes (lentils, chickpeas, dried beans), fruits, and vegetables contain dietary fiber. Whole products (wholemeal bread, wholemeal pasta, whole grain rice) are also rich in fiber.

In practice, it is recommended to eat 5 servings of fruits and vegetables a day (one serving is equivalent to an apple, a tomato, two apricots, a bowl of soup, or homemade compote). Additionally, it is advisable to consume one whole product per day and to eat legumes twice a week.

Limit the consumption of red meats and cold cuts

In practice, it is recommended :

• To limit red meat consumption to less than 500g per week, which is about 3 to 4 steaks (one steak weighing between 100 and 150g).
• To prefer poultry and alternate it with fish, eggs, and legumes.
• To limit the consumption of cold cuts to less than 150g per week

Limit the consumption of fast food and ultra-processed foods rich in fats

There are several types of products to limit : industrial breads and pastries, chocolate bars, snack biscuits, ready-to-eat meals, fast food, instant soups and noodles, meat-based preparations, sugary and fatty snacks and desserts, and sodas (Source: centreleonberard.fr).

Consume dairy products daily

It is advisable to consume two dairy products per day by alternating them. The recommended "dairy products" include milk, milk-based products like yogurts, petits suisses, cottage cheese, and cheeses. They do not include milk-based products that are high in fat (butter, cream) or sugar (dessert creams or ice creams) (Source: Institut national du cancer).

Limit alcohol consumption

In practice, it is recommended that men limit their daily consumption to less than 2 glasses (wine, beer, aperitif) and that women limit their daily consumption to less than one glass (Source: centreleonberard.fr).

Several studies indicate that 16 to 71% of colorectal cancers in Europe and the United States are attributable to lifestyle-related factors. The good news is that many of these factors are modifiable by changing certain habits, such as improving diet and engaging in regular physical activity.