Scientists have long sought a smarter way to fight cancer — one that works with the immune system rather than overwhelming the body with toxins. Now, researchers in Japan may have found a surprising source: the gut of a common tree frog.
A new study published in the journal Science of the Total Environment has revealed that Ewingella americana, a bacterium isolated from the intestines of the Japanese tree frog (Dryophytes japonicus), can completely eliminate colorectal cancer tumors in mice after a single intravenous dose. The research, conducted at the Japan Advanced Institute of Science and Technology (JAIST), has drawn international attention for the boldness of its findings.
In experiments using immunocompetent mouse models of colorectal cancer — meaning mice with fully functional immune systems — every single treated animal achieved complete tumor elimination. Researchers found no cancer recurrence even when the cured mice were later re-exposed to cancer cells, suggesting the treatment had generated lasting immune memory.
That dual mechanism is what makes the discovery so compelling. Ewingella americana appears to attack tumors through two distinct pathways: directly killing cancer cells, and activating the immune system to do the same. The bacterium selectively colonizes tumor tissue — exploiting the nutrient-rich, oxygen-poor environment that tumors create — and triggers a cascade of immune responses that help the body recognize and destroy remaining cancer cells.
The team systematically screened nine bacterial strains isolated from the intestines of two amphibian species — the Japanese tree frog and the Japanese fire-bellied newt (Cynops pyrrhogaster) — as well as a lizard (Takydromus tachydromoides). Of the nine strains tested, Ewingella americana stood out for its remarkable tumor-fighting properties.
Bacteria-based cancer therapies have a surprisingly long history. More than a century ago, surgeon William Coley observed that some cancer patients who developed bacterial infections unexpectedly saw their tumors shrink. Today, intravesical BCG therapy — a type of live bacteria treatment — is the gold standard for early-stage bladder cancer. But applying these principles to solid tumors like colorectal cancer has proven far more difficult.
Recent advances in tumor microbiome research have reinvigorated the field. Scientists now know that bacteria naturally inhabit tumors, and some of these microbes appear to influence treatment outcomes. Ewingella americana represents a new twist: not a microbe already living in tumors, but one that can be strategically introduced to target them from within.
Colorectal cancer is the third most diagnosed cancer worldwide and the second leading cause of cancer-related deaths globally, making new treatment approaches urgently needed. Current standard treatments — surgery, chemotherapy, and radiation — are effective but come with significant side effects and limitations. Immunotherapies have transformed outcomes for some cancers but remain ineffective for many colorectal cases.
The JAIST researchers acknowledge that mouse models do not always translate directly to humans. Further preclinical work, and eventually clinical trials, will be necessary before any bacteria-based treatment could reach patients. But the completeness of the results — 100% tumor elimination with no recurrence — has generated genuine scientific excitement.
For now, the humble tree frog has become an unlikely symbol of cancer research hope. Its gut microbiome, refined by millions of years of evolution in wet and wild environments, may contain exactly the kind of biological tools that human medicine has been searching for.
