Researchers analyzed 243 brain tissue samples (168 tumor, 75 healthy) and identified bacteria living inside both primary and metastatic brain tumors. Using imaging, genomic sequencing, and culturing, the team found bacterial strains that overlap with gut and oral microbes, suggesting possible routes of entry. The bacteria appear to interact with immune cells in the tumor microenvironment and may influence tumor behavior, but the study shows association rather than proof of causation. Further work will explore routes of spread and whether microbes can be targeted therapeutically.
Unexpected Bacteria Found Inside Brain Tumors — Could Microbes Shape Tumor Behavior?
Researchers analyzed 243 brain tissue samples (168 tumor, 75 healthy) and identified bacteria living inside both primary and metastatic brain tumors. Using imaging, genomic sequencing, and culturing, the team found bacterial strains that overlap with gut and oral microbes, suggesting possible routes of entry. The bacteria appear to interact with immune cells in the tumor microenvironment and may influence tumor behavior, but the study shows association rather than proof of causation. Further work will explore routes of spread and whether microbes can be targeted therapeutically.
04:32 AM, 11/19/2025Health
The brain has long been viewed as a largely sterile organ, but new research reports the surprising discovery of bacteria inside brain tumors and suggests those microbes could influence how tumors grow and respond to the immune system.
Study overview
Researchers examined 243 human brain tissue samples from 221 patients, including 168 tumor samples and 75 non-tumor (healthy) brain samples. Using a combination of high-resolution imaging, genomic sequencing and bacterial culture techniques, the team identified bacteria located within both primary brain tumors and metastatic lesions that originated elsewhere in the body.
What the team found
The investigators detected a diversity of bacterial strains inside tumor tissue. Some strains overlapped with microbes commonly found in the gut and oral cavity, prompting questions about potential entry routes to the brain. Laboratory analyses indicated that bacterial elements appear to interact with immune cells in the tumor microenvironment — interactions that could plausibly alter tumor behavior, for instance by modulating inflammation or immune recognition.
“This work opens a new dimension in our understanding of brain tumor biology,” said Dr. Jennifer Wargo, professor of surgical oncology and genomic medicine at the University of Texas MD Anderson Cancer Center. “By mapping how microbial elements influence the brain tumor microenvironment, we may be able to identify new therapeutic strategies to improve outcomes for patients facing these devastating diseases.”
“These findings highlight a previously unknown player in the brain tumor microenvironment — a new piece of the puzzle that may help explain brain tumor behavior,” said lead author Dr. Golnaz Morad, a postdoctoral research fellow in surgical oncology at MD Anderson. “Bacterial elements appear to interact with immune cells within the tumor in ways that could influence how tumors develop and respond to treatment.”
Limitations and next steps
The researchers are investigating how bacteria might reach the brain and whether conditions such as gum disease could contribute to bacterial spread. Importantly, the study demonstrates association and biological plausibility but does not establish that bacteria cause brain tumors or directly accelerate tumor growth. Further experimental and clinical work is needed to determine causality, identify routes of entry, and explore whether targeting these microbes could influence treatment outcomes.
The full research report was published in Nature Medicine.