Why Some Head and Neck Cancer Patients Don't Respond to Immunotherapy—And What Bacteria Have to Do With It

Cleveland Clinic researchers have uncovered a surprising culprit behind immunotherapy treatment failures: bacteria living inside cancerous tumors. Two groundbreaking studies published in Nature Cancer reveal that elevated bacterial levels in head and neck cancer tumors suppress the immune system, making immunotherapy ineffective for many patients.

How Do Bacteria Make Immunotherapy Stop Working?

The research team, led by Dr. Timothy Chan and colleagues, found that higher bacterial levels—regardless of the specific bacterial strains—weaken the body's immune response against cancer. When bacteria accumulate in tumors, they attract neutrophils, white blood cells designed to fight infections. While neutrophils are essential for battling bacterial infections, their presence in cancer tumors actually suppresses the very immune response that immunotherapy needs to work effectively.

"These studies shift the focus of immunotherapy resistance research beyond tumor genetics to unexpected factors like the tumor microbiome," said Timothy Chan, M.D., Ph.D., chair of Cleveland Clinic's Department of Cancer Sciences. "By identifying bacteria as a key barrier to treatment, we're opening the door to new strategies for patient selection and targeted antibiotic therapies, potentially improving outcomes for those who don't benefit from immunotherapy."

What Did the Clinical Trial Data Show?

The researchers validated their findings through multiple approaches, including analysis of the Javelin HN100 Phase III clinical trial. This large-scale study tested whether adding anti-PD-L1 immunotherapy to standard chemoradiotherapy improved outcomes for patients with head and neck squamous cell carcinoma. The results were clear: patients with high tumor bacteria levels had significantly poorer outcomes when treated with immunotherapy compared to standard chemoradiotherapy alone.

Dr. Daniel McGrail's analysis of genetic data from patient tumor samples confirmed that bacterial levels, not specific bacterial types, were the key factor. Meanwhile, Dr. Natalie Silver's preclinical studies provided compelling evidence that antibiotics could reverse this effect—reducing tumor size and improving immune response in laboratory models.

What Does This Mean for Cancer Treatment?

This discovery addresses a critical challenge in cancer care. "Immunotherapy is a promising treatment option for patients with head and neck cancer, but the majority unfortunately do not respond," explained Dr. Silver, director of Head and Neck Cancer Research at Cleveland Clinic. "Our research examines how bacteria influence treatment failure. This can help us identify patients most likely to benefit from immunotherapy, with the goal of avoiding unnecessary risk and exposure."

The research findings suggest several potential improvements to cancer treatment:

• Patient Selection: Testing tumor bacterial levels could help doctors identify which patients are most likely to benefit from immunotherapy before starting treatment
• Antibiotic Therapy: Targeted antibiotic treatments might reduce bacterial levels in tumors, potentially restoring immunotherapy effectiveness
• Personalized Treatment: Understanding each patient's tumor microbiome could lead to more individualized treatment approaches

Building on these discoveries, Dr. Silver has already launched a clinical trial funded by the American Cancer Society and VeloSano to test whether antibiotics can lower tumor bacterial levels and boost immunotherapy response in head and neck cancer patients. Meanwhile, Dr. McGrail is investigating why some tumors harbor more bacteria than others, and Dr. Chan is exploring how bacteria might cause DNA mutations in tumors.

"By uncovering the tumor microbiome's role in immunotherapy resistance, these studies mark a significant step forward in understanding the complex interactions between cancer and the immune system," said Dr. McGrail. "This research broadens our perspective on cancer treatment and paves the way for developing personalized therapies to improve outcomes for patients."