Exposure to toxin increases colorectal cancer risk among younger adults, study finds

Amid the alarming trend of colorectal cancer cases rising among young people, a new study has pinpointed a potential source.

Researchers from University of California San Diego have linked a bacterial toxin called colibactin to the increase in early-onset cases.

Colibactin is produced by certain strains of Escherichia coli (E. coli) that exist in the colon and rectum, according to the researchers.

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Exposure to the bacterial toxin during early childhood can alter the DNA of colon cells in a way that increases the risk of developing colorectal cancer before age 50, the study found.

The study, which was funded by Cancer Research UK, was published in the journal Nature on April 23.

"The key takeaway is that exposure to colibactin is likely a major contributor to early-onset colorectal cancer," senior author Ludmil Alexandrov, professor in the Shu Chien-Gene Lay Department of Bioengineering and the Department of Cellular and Molecular Medicine at UC San Diego, told Fox News Digital.

In the study, the researchers analyzed 981 colorectal cancer genomes from early-onset and late-onset colorectal cancer patients across 11 countries. 

Those who had prior exposure to colibactin were found to have specific mutations in their DNA, which have been shown to mainly occur in the first decade of life — "placing children on an accelerated path to developing cancer as young adults."

That group was 3.3 times more likely to develop early-onset colorectal cancer compared to those who were diagnosed after 70.

These mutations were found to make up 15% of the early genetic alterations that increase colorectal cancer risk.

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"We detected the mutational signature of colibactin in over 50% of colorectal tumors from patients under 40, compared to less than 10% in tumors from older individuals," Alexandrov noted.

"If someone acquires one of these driver mutations by the time they’re 10 years old, they could be decades ahead of schedule for developing colorectal cancer, getting it at age 40 instead of 60," noted Alexandrov.

The fact that a microbial exposure in the first few years of life can leave a "lasting genomic imprint" and likely contribute to cancer in adulthood is both "remarkable and sobering," according to the researcher. 

"It’s a reminder that there are likely many other such exposures we’ve yet to uncover, and that the way we nurture and protect children during these formative years may have long-term implications for their lifelong health," he told Fox News Digital. 

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"From my perspective, investing in early-life prevention, healthy living and research is not just important — it’s essential."

Dr. Emil Lou, MD, PhD, a board-certified oncologist and internal medicine physician at the University of Minnesota, agrees that the microbiome – "the constellation of microbes that includes bacteria that live under normal circumstances in our gut" — is one potential culprit of early-onset colorectal cancer.

"It is less surprising now than it was a decade ago that any form of bacteria – more specifically, a toxin derived from bacteria – could be associated with and potentially be the primary cause of cancer," Lou, who was not involved in the study, told Fox News Digital. 

"What is especially concerning is the long period of time that might lapse between exposure to the bacteria early in life, and the time before the related cancer is diagnosed."

Alexandrov pointed out that the study provides "strong genomic evidence" of a "striking association" between colibactin and early-onset colorectal cancer, but cannot prove causation. 

"Demonstrating unequivocal causality — proving that colibactin alone is sufficient to initiate cancer in humans — remains a significant challenge," he told Fox News Digital.

"Definitive proof of causality would require long-term prospective studies beginning in early childhood to monitor microbial colonization and track cancer development over several decades."

Lou agreed with this limitation, noting the complexity of cancer factors.

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"There are many aspects of our environment – both within and outside of our bodies – that can play a role in development of cancer," he said. "It is difficult to say or conclude whether any given single factor – in this case, the bacteria-derived toxin – is the true or even a major cause of colorectal cancer."

"Providing evidence of potential association sets the foundation for more in-depth studies to determine whether there is true cause and effect," Lou added.

Alexandrov noted that while the findings don’t yet warrant changes to screening or treatment guidelines, they do highlight the "critical role of early-life microbial exposures" in terms of long-term cancer risk. 

"We are actively working on developing screening tests to detect the long-term effects of colibactin exposure, with the goal of translating these findings into practical prevention strategies in the near future," he added.

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Colorectal cancer cases have doubled among adults under 50 for each of the past two decades, statistics show.

"If current trends continue, colorectal cancer is projected to become the leading cause of cancer-related death among young adults by 2030," the researchers concluded.