JUANA SUMMERS, HOST:
Science has made many cancers more treatable and survivable, but colorectal cancer has become more lethal for people at younger ages. NPR's Yuki Noguchi reports doctors have been trying to find out why.
YUKI NOGUCHI, BYLINE: Like so many in her field, Ohio State University oncologist Ning Jin is alarmed by the number of patients in their 30s and 40s with late-stage cancer in their lower digestive tract. It's not just that these patients are decades younger than what had been typical for colorectal cancer. Jin says the tumors themselves are also more stubborn to treat.
NING JIN: Even though we treat young patients more aggressive by chemo, more chemo or more surgery, patients' outcome is not necessarily better.
NOGUCHI: Jin says about a fifth of patients have hereditary markers that increase risk of these cancers. But that doesn't explain the remaining 80% of cases.
JIN: So there must be some environmental factor or changes.
NOGUCHI: Figuring out what's causing more cancers among younger patients is a huge medical mystery. And while detection and treatment are both improving, this rising incidence is undermining that progress, especially when it comes to colorectal cancer. Veteran oncologist John Marshall runs the Lombardi Cancer Center at Georgetown University.
JOHN MARSHALL: Thirty-plus years ago when I first started, no one, no one, zero number of patients were in my clinic under the age of 50 with colon cancer. And now it is in almost half of the patients that I see.
NOGUCHI: And, he says, these earlier onset tumors show up differently, lower in the tract near the rectum. What's causing all these rapid shifts within a generation? Experts have several potential suspects. One is our greater reliance on ultra-processed foods, also on plastics and chemicals that leach into water and our bodies. Plus, we aren't as active. Their prevailing theory is that all of those factors come down to the gut, specifically, says Marshall, the composition of our microbiome and the bacteria and myriad microorganisms living there.
MARSHALL: The way I think of it is it's our soil. It's a very important part of our interface with the world.
NOGUCHI: The function of digestive organs, after all, is to help incorporate things we eat into our bodies.
MARSHALL: What I think is that we have somehow altered the soil in some way, so that it's now causing this phenomenon of colon cancer. It may be causing other diseases, too. But the most striking one is colon cancer.
NOGUCHI: But the microbiome is complex and hard to study. Marshall says our mouth, stomach and gut all have different chemistries that create different microenvironments. And there's no way to test whether they're healthy.
MARSHALL: We don't know how to test it. We don't know how to make a good one.
NOGUCHI: Ning Jin, the Ohio State oncologist, says chemicals like a detergent or a pesticide can strip the mucus lining that protects the gut and helps things move through it. That's a bit like tearing slats from a fence, leaving the gut cells vulnerable.
JIN: The microbes can cause DNA damage and cause leaky gut.
NOGUCHI: To limit the risk of developing cancer, Jin and other physicians advise people to avoid ultra-processed foods, alcohol and smoking, as well as getting regular exercise, and of course, to get regular screenings.
Yuki Noguchi, NPR News.
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