Scientists say they may be one step closer to detecting the cause of the mystery rise in colon cancer in young people.
Researchers have discovered that people with an aggressive form of the disease have unusually high levels of three bacteria in the gut.
Fusobacterium, Clostridium and Shewanella can become more common because of a diet high in processed foods and low in fiber.
Testing for these three bacteria could help to diagnose those most at risk, the authors wrote.
It comes as colon cancer diagnoses among under-50s reach epidemic levels, with nearly 18,000 young adults now told they have the disease every year. For comparison, in 1999 the figure was less than 12,000.
The above graph shows colon cancer cases among under 50s by year. There is a drop in 2020 because the Covid pandemic led to fewer people coming forward for screenings
Kate Middleton, 42, was diagnosed with cancer following abdominal surgery earlier this year
For the study, scientists tested stool samples from 94 colon cancer patients including 24 with a KRAS mutation — which makes the cancer more aggressive.
Of the 26 bacteria species they tested for, the team found three which were more common among those with the more aggressive form of the disease.
Fusobacteriums can cause inflammation in the gut, the researchers warned, while Colstridium — such as C. difficile — can release toxins.
These raise the risk of damage to DNA in cells, which in turn increases the chance that they could turn cancerous.
For Shewanella, this bacteria proliferates on the surface of tumors, the team wrote — helping to support their growth.
Colon cancer is surging among under-50s, with cases of the disease rising 50 percent over two decades to nearly 18,000 per year.
It has also become the number one cause of cancer deaths among men in the age group and the number two cause among women.
Scientists are stumped as to the cause of the uptick, blaming everything from antibiotics to obesity and even a type of fungus.
A $25million global probe has also been launched to attempt to track down the causes.
Young patients diagnosed with colon cancer include Evan White, 24, from Dallas whose tumor was not detected until it had progressed to stage three — when the cancer is harder to treat.
He had been on track to marry his girlfriend and move to California, but he died after a four-year battle with the disease.
Others include Marisa Maddoz, a paralegal from Delaware, who was diagnosed with the disease at the age of 29 years.
She told DailyMail.com that treatment for the cancer has left her unable to have another child.
Kate Middleton, 42, bravely revealed last month that she had also been diagnosed with cancer following abdominal surgery.
She has not revealed the type of cancer that doctors detected, but her comments prompted an outpouring of support — and inspired some cancer survivors to share their stories.
Evan White, from Dallas, was diagnosed with stage three colon cancer at the age of 24 after going into hospital to get an abscess removed from his tonsils. On the right is Marisa Maddox who was diagnosed with the cancer at the age of 29 years, She now can’t have anymore children
Previous studies have suggested patients with more Fusobacteriums in their guts consume more processed meats — sausages, bacon and jerky — refined grains — such as white rice, couscous and cornflakes — and carbonated beverages.
They also consume more red meat, such as steaks, pork chops and beef mince.
And eat less white meat, such as chicken and fish, and fewer fruits, nuts, vegetables and beans.
For Clostridium, studies suggest people who consume high-fat diets — such as a lot of fast food — are more likely to have outbreaks of this bacteria in their gut.
This group includes the bacteria C. difficile, which causes painful blooms in nearly 500,000 Americans every year — triggering symptoms including diarrhea.
Scientists say consuming a diet low in fiber, such as lacking in grains, fruits and vegetables, raises the risk of this bacteria’s population surging in the gut.
Taking antibiotics can also cause this bacteria to proliferate, they said, because the drugs also kill off healthy bacteria in the colon.
Revealing the study, Dr Weizhong Tang said: ‘Our new work contributes to the growing body of evidence highlighting the significance of microbiota-driven mechanisms in cancer pathogenesis.
‘Understanding the specific associations between different types of KRAS mutations and colon cancer is vital.’
In the paper, published in Microbiology Spectrum, the scientists also found that Bifidobacteriums could help to prevent the progression of colon cancer.
The bacteria break down dietary fibers to produce butyrate, which has been shown to have anti-inflammatory and anti-cancer effects.
And a high population of these bacteria is linked to consuming more garlic, leeks and onions — among other vegetables.
In the paper, the researchers also revealed they had tried to make a machine learning model that could use the study results to give personalized treatment recommendations — but they said more work was needed.
Several studies have also previously suggested that imbalances in the gut microbiome could be behind colon cancer.
A paper published in August last year found that a high-fat diet could be behind increased rates.
The researchers, from the Salk Institute and the University of California, San Diego, found that the fat altered the microbiota, causing gut inflammation which raised the risk of the disease.