Scientists at The University of Texas MD Anderson Cancer Center have made an important discovery about why some cancers are so hard to treat.
They found that certain bacteria living inside tumors may actually help cancer cells hide from the body’s defenses and resist treatment.
The study, published in the journal Cancer Cell, focuses on a bacterium called Fusobacterium nucleatum (Fn), which seems to play a key role in protecting cancer cells from chemotherapy and the immune system.
Doctors have long known that bacteria can be found inside some tumors, especially in cancers of the mouth and colon.
But until now, no one really understood what those bacteria were doing there.
The new research reveals that these microbes aren’t just bystanders—they actively change how cancer cells behave.
The team discovered that Fusobacterium can make cancer cells enter a special “resting” phase called quiescence. In this state, the cancer cells stop dividing and become much harder for treatments to kill.
They also become less visible to the immune system, which normally looks for rapidly dividing or abnormal cells to destroy. It’s like the bacteria are teaching the cancer cells to play dead, helping them survive during treatment.
Dr. Susan Bullman, the senior author of the study, said that these bacteria-tumor interactions have been “hiding in plain sight.” With new technology, scientists can now observe how bacteria directly interact with cancer cells and influence tumor behavior.
She believes this discovery opens the door to a new kind of cancer treatment that takes microbes into account.
The researchers used advanced imaging tools to map where the bacteria were located within tumors. They found that Fusobacterium tends to gather in specific areas where cancer cells are tightly packed and less active. These bacterial clusters were especially common in parts of tumors that were not responding well to chemotherapy.
In experiments using mice, the scientists showed that when Fusobacterium was present, the cancer cells were more resistant to treatment. The bacteria seemed to settle between cancer cells, disrupt their communication, and push them into the resting state.
When the bacteria were removed, the cancer cells became more vulnerable to chemotherapy again. This suggests that the process is reversible—meaning that if doctors can target or block the bacteria, they might be able to make cancer cells sensitive to treatment once more.
The team confirmed their findings by analyzing samples from 52 patients with oral and colorectal cancer. They found that tumors with higher levels of Fusobacterium had lower levels of immune activity and weaker responses to treatment. In other words, more bacteria meant tougher tumors.
Understanding how bacteria influence cancer could be a game-changer. Most cancer treatments focus only on human cells, but this study shows that microbes inside the body may also play a major role. If scientists can find ways to remove or control harmful bacteria like Fusobacterium, they could make chemotherapy and immunotherapy more effective.
Researchers at MD Anderson are already exploring how to use bacteria to fight cancer instead of helping it. Their labs are developing special “tumor-targeting” bacteria that could deliver drugs directly to cancer cells. This creative idea, sometimes called “bugs as drugs,” could help overcome the barriers that make solid tumors so difficult to treat.
However, the study does have some limits. The experiments were done in controlled lab settings that don’t fully capture the complexity of the human body. Real tumors are exposed to constantly changing conditions, including oxygen levels and immune responses. Future studies will need to confirm how bacteria behave inside living human tumors.
Overall, this study adds a fascinating new layer to our understanding of cancer biology. It reminds us that cancer doesn’t exist in isolation—it’s influenced by everything in its environment, including microbes.
By learning how bacteria help tumors survive, scientists may one day design smarter, microbe-aware therapies that stop cancer from using bacteria as its secret shield.
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The study is published in Cancer Cell.
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