It’s still not clear why colon cancer cases continue to rise among young people — but researchers may have come across a lead.
A new study has identified a potential culprit: a toxin called colibactin that’s capable of altering DNA. Scientists found that exposure to this gut bacteria in early childhood can lead to mutations within colon cells, which could be what’s causing so many young adults to develop colorectal cancer (CRC).
Here’s a closer look at this fascinating new research and what it tells us about this potential carcinogen.
Colon cancer and gut bacteria
The study, which was published last week in Nature, examined tissue samples from nearly 1,000 CRC patients. The team discovered that colibactin leaves behind a specific pattern of DNA mutations, and that patients who developed the disease before the age of 40 were more than three times as likely to exhibit this genetic hallmark than those who were diagnosed after 70.
The researchers were also able to trace when these mutations arose, and the scientists believe that they’re most likely acquired by the age of 10. That could put these patients “decades ahead of schedule for developing colorectal cancer, getting it at age 40 instead of 60,” the study’s senior author, Ludmil Alexandrov, says.
“This reshapes how we think about cancer,” he says. “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.”
What is colibactin?
Colibactin is a bacterial toxin that’s produced by certain strains of E. coli, which is often referred to as pks-positive. Between 20 to 40 percent of people carry this strain, says Christopher Johnston, associate professor and director of microbial genomics at The University of Texas MD Anderson Cancer Center.
Most healthy adults have a thick layer of mucus that protects their gut cells from this toxin. “Problems arise when this protective barrier is breached,” Dr. Johnston tells us, allowing colibactin to inflict DNA damage.
One thing that may weaken the gut barrier is the modern Western diet, which is high in ultraprocessed foods and low in fiber, Dr. Johnston says. But that’s just one potential contributing factor that researchers have homed in on. Others include the increased use of antibiotics in childhood, rising rates of C-section births (which are thought to disrupt a newborn’s microbiome), and more exposure to environmental toxins.
“It’s suspected that these factors could establish long-term vulnerabilities, making individuals more prone to colorectal cancer decades later,” Dr. Johnston tells us.
He also noted that colibactin is not the only microbe that’s been implicated in CRC. Other studies have looked at a bacteria called Fusobacterium nucleatum, which is typically found in the mouth, and can fuel the growth of cancer cells in the gut.
“It’s unlikely that a single factor is responsible for the rise in early onset cancers,” Dr. Johnston says. “Collectively, lifestyle, environmental, and biological shifts are likely interacting throughout an individual’s lifetime — cumulatively increasing the risk.”
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