A new study reveals that chemotherapy's damage to the gut lining unexpectedly rewires the microbiota, producing a compound that strengthens immune defenses against cancer spread. This process reduces immunosuppressive cells and enhances resistance to metastasis, particularly in the liver. Patient data links higher levels of this compound to improved survival in colorectal cancer cases.
Chemotherapy, notorious for its harsh side effects on the digestive system, may have an unforeseen benefit in fighting cancer's progression. Research shows that the treatment injures the intestinal lining, which disrupts nutrient availability and prompts changes in the gut bacteria composition.
These alterations lead to increased production of indole-3-propionic acid (IPA), a metabolite derived from the amino acid tryptophan. IPA circulates through the bloodstream to the bone marrow, where it influences the development of immune cells. Specifically, it modifies myelopoiesis, decreasing the number of immunosuppressive monocytes that typically aid cancer cells in evading detection and fostering metastatic growth.
"We were surprised by how a side effect often seen as collateral damage of chemotherapy can trigger such a structured systemic response. By reshaping the gut microbiota, chemotherapy sets off a cascade of events that rewires immunity and makes the body less permissive to metastasis," stated Ludivine Bersier, the study's first author.
This immune shift enhances T cell function and alters interactions at potential metastatic sites, creating an environment resistant to tumor colonization, especially in the liver. Preclinical models demonstrate these effects clearly.
Supporting evidence comes from clinical data gathered in partnership with Dr. Thibaud Koessler at Geneva University Hospitals. In colorectal cancer patients, elevated IPA levels post-chemotherapy correlated with reduced monocytes and better survival rates.
"This work shows that the effects of chemotherapy extend far beyond the tumor itself. By uncovering a functional axis linking the gut, the bone marrow, and metastatic sites, we highlight systemic mechanisms that could be harnessed to durably limit metastatic progression," remarked Tatiana Petrova, the corresponding author.
Funded by organizations like the Swiss National Science Foundation and the Swiss Cancer League, the study suggests potential for microbiota-derived metabolites in enhancing cancer treatments. Published in Nature Communications in 2025, it proposes a gut-bone marrow-liver axis that could explain chemotherapy's long-term anti-metastatic effects.
