Increased colorectal cancer in young people linked to a childhood bacterial infection

BarcelonaChildhood exposure to a toxic molecule called colibactin could be a new marker for early colorectal cancer.Escherichia coli, Present primarily in the colon and rectum, these bacteria have the ability to alter cell DNA. According to these researchers, the bacteria may be behind the "colorectal cancer epidemic" in people under fifty.

A study published this Wednesday in the journal Nature suggests that colibactin can imprint a genetic signature on the DNA of colon cells during early childhood. Over the years, the scientists note, colorectal cancer-related mutations increase substantially in those under the age of 50 who came into contact with the bacteria. "If someone acquires one of these driver mutations at age 10, they could be decades ahead of developing colorectal cancer and suffer from it at age 40 instead of 60," says Ludmil Alexandrov of the University of California, San Diego, and lead author of the study.

If the upward trend continues, colorectal cancer could be the leading cause of cancer death in young adults by 2030. The reason for this increase, however, is unknown. It is known that young people with the disease usually have no family history and have few known risk factors such as obesity or hypertension. For this reason, the international team sought possible causes among environmental carcinogens or microbial infections.

Researchers, led by Marcos Díaz Gay, the new head of the Digital Genomics Group at the Spanish National Cancer Research Centre (CNIO), have analyzed 981 genomes of patients with colorectal cancer from eleven countries in Europe, America, and Asia and have identified their DNA. According to the research, these signatures are up to three times more frequent in adults under 40 than in those diagnosed after the age of seventy.

"These mutational signatures are a kind of historical record in the genome," says Alexandrov. According to this researcher, the new study "firmly" supports the hypothesis that colibactin-producing bacteria could be silently colonizing the colons of children, initiating molecular changes in their DNA and preparing the ground for colorectal cancer long before the onset of symptoms.

Focus on the first years of life

This study is the first to show a substantial increase in colibactin-related mutations in colorectal cancer cases in people under the age of 50, although it doesn't address how to prevent or combat infection from colibactin-producing bacteria. The finding, in fact, was serendipitous. "Our goal was to examine global patterns of colorectal cancer to understand why some countries have much higher rates than others. But as we delved deeper into the data, one of the most interesting and striking findings was how frequently colibactin-related mutations occurred in early-onset cases," she said.

The next step is to identify how children are exposed to colibactin-producing bacteria and what can be done to prevent or mitigate this exposure. For example, whether there are specific diets or lifestyles that are more conducive to colibactin production, or whether there are variations from country to country, which would require region-specific prevention strategies. For Alexandrov, the conceptual shift this new study represents is that many cancers can be traced to environmental or microbial exposures in early life, long before diagnosis. "This changes the way we think about cancer. It's not just about what happens in adulthood, but also in the first decade of life, perhaps even in the first few years," he concludes.