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Key Points

• Colorectal cancer diagnoses are rising among younger people, and new research suggests that early-life exposure to colibactin, a toxin produced by certain E. coli strains, may contribute to this trend.
• Researchers found that colibactin-related mutations were 3.3 times more common in early-onset colorectal cancer cases than in late-onset cases.
• Researchers are continuing to study how childhood microbiome factors, including exposure to colibactin-producing bacteria, may influence colorectal cancer risk later in life.

Colorectal cancer, which the Cancer Research Institute explained was “once considered a disease of older age,” is skyrocketing among younger people. According to the institute, 1 in 5 diagnoses now occurs in someone under 55, and the disease is quickly becoming “a leading cause of cancer-related death in young people.” While a number of factors are at play, one study suggests that E. coli could play a major role. 

In 2025, researchers led by a team at the University of California, San Diego published their study in the journal Nature, which outlined how colibactin, a toxin produced by certain strains of E. coli that appears to damage DNA early in childhood, could be fueling this colon cancer crisis.

To identify this connection, the team examined the colorectal cancer genomes of 981 patients with either early- or late-onset colon cancer. They found that colibactin-related mutations were 3.3 times more common in patients with early-onset colon cancer than in those with late-onset.

“These mutation patterns are a kind of historical record in the genome, and they point to early-life exposure to colibactin as a driving force behind early-onset disease,” said Ludmil Alexandrov, the study’s senior author and a professor in the Shu Chien-Gene Lay Department of Bioengineering and the Department of Cellular and Molecular Medicine at UC San Diego, in a press release. “If someone acquires one of these driver mutations by the time they’re 10 years old,” he added, “they could be decades ahead of schedule for developing colorectal cancer, getting it at age 40 instead of 60.”

Alexandrov also explained to NPR that the team found colibactin mutations were far less common in places like rural Africa and Asia, but turned up more often in the U.S. and Western Europe. That, he added, could be due to a number of factors, including the use of antibiotics and childhood nutrition choices, as well as whether someone was breastfed and how they were delivered, either by cesarean section or vaginal delivery. 

“All of these factors are known to substantially affect the microbiome, and there is some evidence they may impact this [colibactin-producing] bacteria, but we really need to investigate each one carefully,” the researcher said. 

It’s important to note that if you do contract this particular strain and have this particular toxin in your body, it doesn’t mean you’ll automatically get colon cancer.

“We don’t have definitive data on whether having the toxin means you will definitely get young-onset colorectal cancer: this study only looked at cancers themselves, not at the bowels of healthy people without cancer,” Trevor Graham, a professor of genomics and evolution and director of the Center for Evolution and Cancer at The Institute of Cancer Research, who was not involved in the study, said in a statement. “So, it’s quite possible that [this certain] E. coli are very common and only a few people with the ‘bad bugs’ will actually go on to get bowel cancer.”

Graham added, “I think it is very likely cancer only occurs in some cases, because even though someone might have the ‘bad bugs’ that cause mutations, those bugs have to cause the right mutations to make a cancer grow.” 

While this strain of E. coli may be a player in the game, it’s only a piece of the ever-growing colorectal puzzle. The Cancer Research Institute noted that several risk factors are at play, not the least of which is genetics. There are, however, things the institute said you can control, including your lifestyle.

“A diet high in processed and red meats and low in fiber, fruits, and vegetables is associated with increased colorectal cancer risk,” the Institute said. It cited The World Cancer Research Fund’s recommendations to limit red meat to 12–18 ounces per week and minimize processed meats to reduce your risk. Additionally, you may want to cut back on alcohol, as the institute also said that “heavy alcohol consumption” can increase risk.

For now, Alexandrov said in the statement that the team is continuing to investigate the issue and exploring whether probiotics could eliminate these and other harmful bacterial strains. The team is also developing early-detection tests that analyze stool samples for colibactin-related mutations and continues to monitor how colorectal cancers are evolving around the world to better understand what we can control in cancer risk. “This reshapes how we think about cancer,” he said. “It might not be just about what happens in adulthood — cancer could potentially be influenced by events in early life, perhaps even the first few years. Sustained investment in this type of research will be critical to the global effort to prevent and treat cancer before it’s too late.”

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