Childhood exposure to a bacterial toxin in the colon may be triggering the increase in colorectal cancer cases among younger patients, a new study suggests.
Once considered a disease of older adults, colorectal cancer is now on the rise among young people in at least 27 countries. Its incidence in adults under 50 has roughly doubled every decade for the past 20 years.
Looking for clues as to why, the researchers analyzed genes of 981 colorectal cancer tumors from patients with varying colorectal cancer risk levels who had early- or late-onset disease in 11 countries.
DNA mutations in colon cells that are known to be caused by a toxin produced by Escherichia coli, called colibactin, were 3.3 times more common in adults who developed colon cancer before age 40 than in those diagnosed after age 70.
The patterns of mutations are thought to arise when children are exposed to colibactin before age 10, researchers reported in Nature.
The mutation patterns were particularly prevalent in countries with a high incidence of early-onset cases.
"If someone acquires one of these... 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," study leader Ludmil Alexandrov of UC San Diego said in a statement.
"Not every environmental factor or behavior we study leaves a mark on our genome," said Alexandrov. "But we've found that colibactin is one of those that can. In this case, its genetic imprint appears to be strongly associated with colorectal cancers in young adults."
The researchers have found other mutational signatures in colorectal cancers from specific countries, particularly Argentina, Brazil, Colombia, Russia and Thailand.
This suggests that local environmental exposures may also contribute to cancer risk, they said.
"It's possible that different countries have different unknown causes," study co-author Marcos Diaz-Gay of the Spanish National Cancer Research Center in Madrid said in a statement.
"That could open up the potential for targeted, region-specific prevention strategies."
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