Bacterial toxin theory for bowel cancer rise in youth
Experts believe the finding could help explain why rates of bowel cancer are rising among young people across the globe.
The bacterial toxin - called colibactin - is capable of altering DNA and is produced by a strain of E.coli, though not the strain linked to infection such as diarrhoea in some people.
Researchers, including from the UK and backed by Cancer Research UK, found exposure to colibactin in early childhood imprints a genetic signature on the DNA of bowel cells, which may then increase the risk of developing bowel cancer before the age of 50.
Work has been ongoing to discover why more younger people are developing bowel cancer, with experts believing poor diet, more ultra-processed foods, obesity and a lack of exercise are playing a role.
Now in the latest study, led by the University of California San Diego (UCSD) and published in the journal Nature, researchers have uncovered another possible culprit.
Experts examined 981 colorectal (bowel) cancer genomes from patients with both early and late-onset disease in 11 different countries.
They found colibactin can leave behind specific patterns of DNA mutations that are 3.3 times more common in early-onset bowel cancer cases (in the study this was adults under 40) than in those diagnosed after the age of 70.
These mutation patterns were also particularly common in countries with a higher rate of early-onset bowel cancer.
Senior author Ludmil Alexandrov, a professor at UCSD, said: "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."
The study also found that colibactin-related mutations account for around 15 per cent of what are known as APC driver mutations, some of the earliest genetic alterations that directly promote cancer development, in bowel cancer.
"If someone acquires one of these driver 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," Professor Alexandrov said.
The work is part of Cancer Grand Challenges team Mutographs, funded by Cancer Research UK.
Researchers are now developing early detection tests that analyse stool samples for colibactin-related mutations.
Professor Sir Mike Stratton, Mutographs team lead and senior group leader at the Wellcome Sanger Institute, said preventative measures can be explored if this turns out to be correct.
"We know that diet and lifestyle choices drive the risk of developing colorectal cancer, but this study has opened up a new and exciting route we can take when researching how to lower the rate of early-onset colorectal cancer."
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