The number of people under 55 diagnosed with colorectal cancer doubled from 1995 to 2019, a trend that has troubled public-health officials and confounded scientists. Now, researchers from the University of California, San Diego, have unearthed a possible explanation.
Their findings, published in the journal Nature, suggest that a “genotoxin” produced by certain strains of bacteria, including E. coli, may be linked to the rise of these early-onset cancer cases. The toxin, colibactin, can attack cells in the gut of a young person and cause gene mutations that increase the risk of developing the disease.
Think of it as one bacteria’s weapon system for defending itself from other harmful bacteria, explains lead study author Ludmil Alexandrov, PhD, in an NPR interview.
Alexandrov and his team studied tissue samples from nearly 1,000 colorectal cancer patients across four continents. They discovered that these gene mutations were three to five times more prevalent in patients under age 40 than among those 70 or older. The colibactin attacks, they concluded, are occurring during childhood — when E. coli and its siblings dominate the gut microbiome — and manifesting as disease in middle age.
“Our estimate is that it happens within the first 10 years of life,” Alexandrov says. “So if you get that mutation at age 5, that puts you 20 to 30 years ahead of schedule for getting colorectal cancer.”
Researchers noted that the prevalence of this early-onset cancer was much lower in “rural, nonindustrialized” areas of Africa and Asia than in the United States and Western Europe. That suggests diet and other lifestyle factors may be at play.
“All of these factors are known to substantially affect the microbiome, and there is some evidence they may impact this [colibactin-producing] bacteria,” Alexandrov notes. “But we really need to investigate each one carefully.”
