A MARTÍNEZ: More young people are developing colorectal cancer. That's cancer that originates in the colon or rectum. According to research published in the journal Nature yesterday, a harmful bacteria could be the reason why. Here's NPR's Will Stone.
WILL STONE, BYLINE: It's unclear why colon cancer cases have doubled in people under 55 over the past two decades, but part of the story could be colibactin. It's known as a genotoxin, and it's made by certain strains of E. coli and other bacteria. Ludmil Alexandrov is a researcher at the University of California San Diego.
LUDMIL ALEXANDROV: We can think of it as the weapon system of a bacteria. You know, they need to fight other bacteria. They need to defend themselves.
STONE: They do this by damaging DNA. And the thinking goes, this colibactin weaponry sometimes gets directed at our own gut cells.
LUDMIL ALEXANDROV: And they may end up actually causing colorectal cancer.
STONE: Scientists can look for mutations in colon cancer - signs that colibactin did the damage - and they find them in about 15% of cases. But when Alexandrov and a team of scientists analyzed samples from nearly 1,000 patients all over the world, they discovered that number is actually much higher in younger people.
LUDMIL ALEXANDROV: The thing that we very strikingly saw is that if we look at people, let's say, under the age of 40 and we compare them to people over the age of 70, they're going to have three to five times more mutations.
STONE: And through some detective work, Alexandrov says they could tell bacteria released the toxins in the gut of these cancer patients when they were kids.
LUDMIL ALEXANDROV: Our estimate is that it happens within the first 10 years of life.
STONE: And that puts people on track to develop cancer maybe in their 20s or 30s instead of later in life. The research can't prove this is what caused early-onset colon cancer in the patients, but it's a strong association. Christian Jobin, a microbiome researcher at the University of Florida, says it builds on years of research, including experiments in animals showing this genotoxin, colibactin, can drive cancer. Of course, the big question here is why.
CHRISTIAN JOBIN: What triggers this weapon or the deployment? We don't know. These E. coli have been there for eon. This is not new. We're not infected. We've been transmitting this E. coli for a long time.
STONE: Around 20% or 30% of people have these strains of E. coli in their gut. But in some people, something about our modern environment, lifestyle, diet and other factors is causing these microbes to behave differently. Alexandrov speculates it could be the mode of birth, breastfeeding, even antibiotics. And it's not just E. coli. Jobin says there are likely other bacteria and genotoxins involved.
JOBIN: I don't think colorectal cancer is caused by a single bacteria producing one genotoxin.
STONE: That, he says, would be too simple.
Will Stone, NPR News.
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