- Gut bacteria could play a role in how cancer patients respond to new treatments.
- Researchers sequenced the microbiomes of patients receiving immunotherapy and found bacterial signatures associated with good and bad outcomes.
- The harmful bacteria seemed to play a greater role, especially a year after starting treatment.
Immune therapies have revolutionized cancer treatment in recent years, but there's still a lot to be discovered in terms of how well they work for individual patients.
Researchers from cancer centers across the US took a close look at patients with melanoma, a form of skin cancer, who were receiving a cutting-edge form of therapy. According to their findings, published in Nature Medicine Monday, each patient's gut bacteria may have played a role in how they responded to treatment.
Collaborators from Oregon State University, the National Cancer Institute, the Frederick National Laboratory for Cancer Research and the University of Pittsburgh recruited 94 participants who were prescribed a treatment called anti-programmed cell death protein therapy, or anti-PD-1, to stop their melanoma from spreading
After collecting stool samples from patients who were either undergoing the treatment or had recently completed it, researchers compared how people with different "microbiotypes," or gut bacteria profiles, responded to the same treatment.
They found that melanoma patients who had an abundance of Lachnospiraceae species — which make up the core of naturally-occurring gut bacteria — tended to respond relatively well to immunotherapy.
On the other hand, those whose guts had been colonized by Streptococcaceae species — also linked to unfavorable responses to gut cancers and liver disease — fared relatively worse and had a greater likelihood of adverse immune reactions. The researchers noted that these bacteria seemed to have a stronger effect than the helpful bugs.
Helpful bacteria in the gut work with the immune system
The human gut microbiome is a complex community of more than 10 trillion microbes from roughly 1,000 different bacterial species — some friendlier than others.
Gut bacteria exist to break down food, pull out nutrients, and help the body respond to immune threats, among other functions. According to the National Center for Health Research, many of these bacteria act as a "tuning fork" for the immune system, making sure it responds to invaders but does not overreact.
However, the gut microbiome operates on a delicate balance. Even taking an antibiotic to treat an infection can throw off that balance by killing some helpful bacteria, which may result in harmful bacteria overwhelming the microbiome.
Microbiome screenings could become a part of cancer treatment
More research needs to be done before scientists can say whether bacteria in the gut directly influenced patients' treatment outcomes, but it's possible that this link could help inform cancer treatment plans in the future.
The study found that the gut microbiota played a particularly crucial role in the response to immune therapy a year into treatment, as observed in patients tested 4 months or more after completing their course of therapy.
Going forward, sequencing the microbiome before a patient is prescribed immunotherapy could help predict on how they might respond to the treatment, or at least shed some light on why some patients respond better than others.