Researchers studying tumour samples from patients in 11 countries have identified a microbial toxin as a potential factor in the growing number of colorectal cancer cases among people under 50. The toxin, produced by gut bacteria, was found to damage DNA and may contribute to the development of early-onset cancer.
Microbial Mutations Linked to Diet-Driven Cancer Risk
Ludmil Alexandrov, a professor at the University of California, San Diego, led the study published in Nature in April 2025. The research identified mutational patterns in tumour DNA caused by colibactin, a genotoxin produced by certain E. coli strains that proliferate in diets high in ultraprocessed foods.
The results arrive as health officials anticipate colorectal cancer becoming the top cause of cancer-related deaths among young adults by 2030. “These findings may also point to new prevention strategies,” the researchers wrote, citing the microbiome’s emerging role in future cancer assessments.
A Rising Threat
According to the study, the slow progression has prompted calls for updated screening guidelines. Global cancer statistics place colorectal cancer as the second most deadly cancer, but recent patterns in younger age groups point to a more pressing threat.
Projections show it could become the top cancer killer among young adults by 2030. The delayed diagnosis plays a key role, with early-stage cases frequently missed. “Often symptomless in its early forms, colon cancer typically begins as polyps and can take ten to 15 years to develop,”
The Microbial Fingerprint of a Cancer
A genomic study of 981 colorectal tumour samples has revealed that two colibactin-related mutational signatures—SBS88 and ID18—were significantly more common in patients under 40. These signatures were found to occur 3.3 times more frequently than in those over 70. “A toxin produced by certain strains of E. coli, whose growth is encouraged by highly processed diets, may lay the groundwork for aggressive bowel cancers decades later,” researchers said.
The toxin was shown to affect specific genes, particularly APC, a key tumour suppressor. “In colibactin-positive cancers, about 25% of APC mutations bore the toxin’s unique signature,” the study stated.
Geography of a Microbial Risk
The study uncovered regional differences in mutational patterns tied to the bacterial toxin colibactin. Countries such as Argentina, Brazil, and Russia, where early-onset colorectal cancer is increasing, had tumour samples with higher levels of toxin-related DNA damage.
Other countries such as Japan and South Korea has shown more stable cancer trends, showed distinct mutational profiles. “This may reflect regional differences in gut microbiomes influenced by diet (particularly ultraprocessed foods), antibiotic use and environmental factors,” the researchers noted. These contrasts suggest a complex interaction between environment, microbiome, and cancer susceptibility.
A Critical Window in Childhood
Researchers have identified a potential early-life window when the gut may be most susceptible to colibactin-related damage. The study found that genetic signatures of the toxin could appear “within the first ten years of life,” long before disease becomes clinically visible.
During this period, the gut microbiome is still developing, leaving it more exposed to lasting microbial effects. Dietary quality, antibiotic exposure, and reduced contact with microbial diversity in urban settings were cited as possible contributors. “Unlike lifestyle risks that build up over decades, colibactin seems to strike during a narrow window,” researchers said.
Implications for Prevention
Insights from the study may prompt changes in early detection and prevention of colorectal cancer. Researchers propose using stool tests to screen for colibactin-producing bacteria in the gut. Diet is also under renewed focus, with evidence linking fibre-rich, minimally processed food to a more balanced microbiome.
“Diets high in fibre and low in processed foods might promote a healthier gut microbiome, potentially suppressing harmful bacteria,” the study stated.
The findings are contributing to ongoing public health discussions about revising screening guidelines to catch more cases in younger populations.
Conclusion
The study leaves open key questions about individual vulnerability to colibactin-linked cancers. Scientists are exploring how genetic predisposition and environmental context interact with microbial exposure, and whether large-scale interventions can reduce the risk.
“The colorectal cancer epidemic of the 21st century may have begun with silent microbial battles in our guts, decades before diagnosis,” researchers stated.