Scientists at the Cleveland Clinic have made an important discovery about cancer treatment. They found that bacteria living inside tumors may explain why some patients respond to immunotherapy while others do not.
Their findings, published in two studies in Nature Cancer, focus on patients with head and neck cancer.
Immunotherapy is a type of treatment that helps the body’s own immune system fight cancer. It has been life-changing for many people, but unfortunately, it does not work for everyone. These new studies show that bacteria in the tumor’s environment can block the immune system’s response, making immunotherapy less effective.
Dr. Timothy Chan, chair of the Department of Cancer Sciences at the Cleveland Clinic, led one of the studies. He explained that these results shift the focus from just looking at the genes in tumors to also paying attention to the bacteria around them.
This could help doctors better choose which patients are more likely to benefit from immunotherapy and even create new treatments that include antibiotics to target the bacteria.
The research team included Dr. Daniel McGrail, Dr. Natalie Silver, and other experts. They used tumor samples from patients, animal models, and data from clinical trials to confirm their findings.
Dr. McGrail studied genetic data and found that high levels of bacteria—not specific types, just higher amounts—were linked to weaker immune responses. Dr. Silver tested this in animal models and showed that antibiotics helped shrink tumors and improved the immune response, while adding more bacteria made tumors resistant to immunotherapy.
The team also worked with Dr. Renata Ferrarotto from the University of Texas MD Anderson Cancer Center. They looked at samples from patients in a clinical trial and found the same pattern: more bacteria in the tumors meant a lower chance that immunotherapy would work.
Dr. Silver explained that even though immunotherapy offers hope to people with head and neck cancer, most patients don’t benefit from it. Their research helps explain why and may lead to better ways to find out who will respond to treatment. The goal is to avoid giving people treatments that won’t help and to develop ways to make immunotherapy more effective for everyone.
In the second study, Dr. Chan and his team analyzed data from a large clinical trial called Javelin HN100. This trial tested whether combining immunotherapy with standard treatments like chemotherapy and radiation would help more people with head and neck cancer.
The analysis showed that people with higher bacteria levels in their tumors had worse results when given immunotherapy.
The studies also showed that high levels of bacteria bring in neutrophils—white blood cells that normally fight infections. But in cancer, these cells can actually block the immune system from attacking the tumor. This makes it harder for immunotherapy to work.
These findings could lead to many new research ideas. For example, why do some tumors have more bacteria? How do these bacteria get into the tumor? Can we change the bacteria to make treatment work better?
Dr. Silver has already started a clinical trial to test whether antibiotics can lower bacteria levels in tumors and improve the results of immunotherapy. At the same time, Dr. McGrail is studying how bacteria might affect the early stages of cancer, and Dr. Chan is looking at how bacteria could cause DNA changes in tumors.
This research is a big step forward in understanding how cancer and the immune system interact. By learning more about the role of bacteria in tumors, doctors may be able to create better, more personalized treatments in the future.
If you care about cancer, please read studies that artificial sweeteners are linked to higher cancer risk, and how drinking milk affects risks of heart disease and cancer.
For more health information, please see recent studies about the best time to take vitamins to prevent heart disease, and results showing vitamin D supplements strongly reduces cancer death.
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