2023-04-30 04:00:00
The latest Canadian and American data confirm it: younger and younger populations are increasingly at risk of developing colorectal cancer. And doctors are looking for explanations.
It’s a story that repeats itself.
The story of men and women often in great shape, who have not yet reached their mid-fifties. The story of symptoms that make their appearance. Some abdominal cramps. Weight loss. Blood in the stool.
At that age, it’s nothing serious, they say. Maybe stress or hemorrhoids.
But the months pass and the symptoms persist. A colonoscopy is required.
Then, the verdict falls, like a cold shower: colorectal cancer, advanced stage.
This story, Catherine Dubé has seen and reviewed it in recent years. The gastroenterologist is the clinical lead for Ontario’s colorectal screening program.
“It’s always a great shock to see such young cancer patients,” she insists. These diagnoses are remembered all our lives. »
The shock has been more and more frequent in recent decades. Diagnoses of early colorectal cancers are rising rapidly in many parts of the world. According to a recent report by the American Cancer Society (ACS), the number of cases among people under the age of 55 has been increasing by 1-2% each year in the United States since 1995.
In Canada, the annual increase in the different types of colorectal cancer among 20 to 49 year olds varied between 1 and 4% from 2000 to 2017, according to the latest data published in The American Journal of Gastroenterology (these calculations exclude Quebec, due to lack of data). Same story in most industrialized countries.
How to explain this phenomenon ? The question is on everyone’s lips among gastroenterologists.
PHOTO PROVIDED BY CATHERINE DUBÉ
The Dre Catherine Dubé, gastroenterologist
We talk regarding it a lot during meetings with our colleagues around the world. We are all alarmed by this situation. Everyone wants to understand what is going on.
The Dre Catherine Dubé, gastroenterologist
Cohort effect
In Canada, colorectal cancer is the third most common cancer, according to the Canadian Cancer Society.
Older people remain significantly more at risk, notes the ACS in its report. Each year, among those 65 and older, 161 out of 100,000 people are diagnosed, compared to 69 out of 100,000 people aged 50 to 64 and 12 out of 100,000 people aged 20 to 49.
However, the increase in cases among the youngest coincides with a decrease observed among the oldest, in particular due to the best preventive measures.
“There is an increased risk for people born following the 1950s, which is called a cohort effect,” says Rebecca Siegel, scientific director of the ACS and co-author of the report. “We are trying to understand the changes in the products to which populations have been exposed over these years. »
“It must also be said that this type of cancer takes 10 to 15 years to develop,” adds the scientist. So when you see 30-year-olds diagnosed, that means they’ve been exposed [à des facteurs de risque] early in their life. »
Changing lifestyles
Unraveling the mystery of early colorectal cancer will be a major challenge, notes Manuela Santos, professor in the Department of Medicine at the University of Montreal. “You would have to follow a really large population and monitor, for example, diet and exposure to environmental factors over a long period of time to see if, 10 years later, people are developing cancer. It is difficult and expensive. »
To provide some possible explanations, the researcher, affiliated with the Montreal Cancer Institute, relies on the study of the intestinal microbiota. This set of microorganisms has been particularly affected by the growing consumption of antibiotics among young people over the past few decades.
CHUM MULTIMEDIA PRODUCTION PHOTO, PROVIDED BY MANUELA SANTOS
Manuela Santos, professor in the Department of Medicine at the University of Montreal
The microbiota is a balance between beneficial bacteria and others that are not good at all. The good bacteria can suppress the harmful effects of the bad ones. But with antibiotics, you kill a large portion of the beneficial bacteria, which creates an imbalance.
Manuela Santos, professor in the Department of Medicine at the University of Montreal
Changes in eating habits have also caused transformations in the microbiota. The consumption of sugary drinks or processed products, for example, are risk factors for colorectal cancer, according to several studies.
Also in the dock are environmental toxins, which can damage the colon.
Better to prevent
Cases of colorectal cancer in young people are not only more frequent. They are also diagnosed at more advanced stages, according to data from the ACS.
A study published in 2017 by researchers at Stanford University, California, also reveals that in people under 50, the diagnosis falls on average 40% later than in older people.
“Young people generally wait longer before seeing a doctor,” explains Rebecca Siegel. And even doctors often think it’s nothing major, given their age. »
PHOTO JEAN-PAUL PELISSIER, REUTERS ARCHIVES
Several countries opt for early detection of colorectal cancer.
When the disease is detected early, the survival rate increases dramatically, from 12% when diagnosed at stage 4 to 92% when diagnosed at stage 1, according to the Canadian Cancer Society. A lesion can also be discovered and removed even before it turns into a tumour.
Several countries have therefore set their sights on screening in an attempt to offset the increase in cases. In 2021, the United States lowered the age for starting screening to 45 years old, rather than 50 years old.
In Quebec, a motion adopted by the National Assembly at the beginning of April urges the government to deploy a systematic screening program. The province is the only one in Canada that does not have this type of program.
The association of gastroenterologists of Quebec has been requesting it for several years now, without success. Another story repeating itself.
Learn more
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- 26 900
- Number of Canadians who were diagnosed with colorectal cancer in 2020.
SOURCE: Canadian Cancer Society
- 67 %
- Probability of surviving at least five years following a diagnosis of colorectal cancer in Canada.
Source: Canadian Cancer Society
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- 20 %
- Proportion of colorectal cancer diagnoses that occur in people under age 55 in the United States, as of 2019. In 1995, this proportion was 11%.
Source: American Cancer Society
- 3 times
- The mortality rate associated with colorectal cancer in the United States is three times higher in Alaska Native communities than among white populations, in particular due to difficulties in accessing health care and healthy food.
Source: American Cancer Society
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