Certain bacteria that cause plaque may be behind treatment-resistant colorectal cancer. study It was published in Nature found on Wednesday.
This particular bacterium is thought to protect tumor cells from cancer-fighting drugs and was found in 50% of tumors examined in the study. Experts say the discovery could pave the way for new treatments and perhaps new screening methods.
Colon cancer is the second leading cause of cancer death in the United States and is expected to cause more than 53,000 deaths nationwide in 2024. American Cancer Society.
Incidence rises sharply among young people: proportion of people under 55 diagnosed with colon cancer almost doubled Between 1995 and 2019, it jumped from 11% to 20% of cases. Additionally, these cases are often diagnosed at a later, more aggressive stage.
Experts still struggle to explain this change.
“Colorectal cancer is highly treatable if caught early, but cases are increasing in younger people, and we don’t know why,” said Dr. McConnell, a surgical oncologist and director at Oregon Health & Science University’s Knight Cancer Institute. says physician Dr. Flavio Rocha. , was not involved in the study.
The new study doesn’t answer that question. It is too early to assume that this bacterium is responsible for the increase in cases among young people. Additionally, most of the patients in the study were over 50 years old.
However, the new study raises “the question of whether levels of this bacterium are elevated in young-onset colorectal cancer, which is on the rise worldwide for unknown reasons,” the researchers say. said lead author Susan Bulman, assistant professor of human biology. Fred Hutchinson Cancer Center in Seattle.
Bacteria with a secret
Scientists have suspected a link between this bacterium, called Fusobacterium nucleatum, and the growth of colorectal cancer for nearly a decade. This bacteria is usually only found in the mouth, far from the colon.
In the mouth, it is one of the most common types of disease-causing bacteria and is associated with periodontal disease and plaque buildup. However, it was unclear how these bacteria could survive intestinal transit and eventually invade tumor cells in places in the body where these bacteria normally do not survive.
In the study, Bulman and his colleagues looked at the bacterial composition of about 200 colorectal tumors and stool samples from more than 1,200 people, half of whom were free of cancer.
What they learned was that bacteria are a little more complex than previously thought. So there are two different variants of this, one of which seems to protect colorectal tumors from chemotherapy.
“It acts like a cloak,” Bulman says.
Normally, immune cells called T cells recognize and attack tumor cells. However, this bacterium recruits another type of immune cell to cancer cells, allowing them to evade T cells.
This stealth variant was present in 50% of colorectal tumors collected in the study. The corresponding stool samples had increased abundance of the variant compared to their healthy counterparts.
“Patients with high concentrations of this bacterium within their colorectal tumors have a much worse prognosis,” Professor Bulman said. “They respond less well to chemotherapy and are at higher risk of recurrence.”
This variant can also cause cancer to develop in the first place.
When Bulman and her team transplanted this variant into mice, it appeared to cause the formation of precancerous polyps, one of the first warning signs of colorectal cancer, but this causal relationship has not been shown in humans. It hasn’t been proven yet, she added.
The researchers also discovered clues that answer the question of how Fusobacterium nucleatum is able to reach the colon in the first place. The bacteria appears to be able to survive the journey through the stomach, taking what scientists previously thought was a toxic dose. Stomach acid.
New treatment goals
Dr. Michael White, assistant professor of colorectal surgery at the University of Texas MD Anderson Cancer Center in Houston, said the discovery of this variant has significant implications for targeted therapies already in place.
“There is evidence that if you remove these bacteria, you get more responses during treatment,” said White, who was not involved in the new study. He says a clinical trial will soon test whether treating patients with antibiotics before chemotherapy induces a better response.
Learning more about which bacterial subspecies, including Fusobacterium nucleatum, are dangerous will allow for a more targeted approach, he said.
That could include prevention.
Scientists identified this variant while it was in the mouth and gave people antibiotics at that point to eradicate the variant before it reaches the colon, Bulman said. He said it was possible. Even if antibiotics don’t successfully remove bacteria from the mouth, their presence may be an indicator that someone is at high risk for developing advanced colon cancer. There is, she added.
Rocha agreed. In the future, he said, some colorectal cancer tests could be as simple as oral swabs.
Understanding the newly identified subspecies could lead to the development of new antibiotics that specifically target this bacterial subtype, rather than eradicating both forms of the bacteria or all bacteria in the mouth. There is also.
There is also the possibility that bacteria may be used to fight cancer.
Because this subtype has already been shown to be able to invade cancer cells very easily, it may be possible to genetically engineer the bacteria to deliver cancer drugs directly to tumors, Bulman said. .
Rocha said researchers are just beginning to scratch the surface of how a person’s microbiome plays a role in an individual’s cancer risk, but this is the most studied in cancer research today. This is one of the most important concepts.
