Gut bacteria patterns predict melanoma relapse with high accuracy
Researchers have identified a strong link between gut bacteria composition and the risk of melanoma returning after treatment, offering a new tool to guide clinical decisions before therapy begins. The findings show that specific microbial profiles in the intestine can predict cancer recurrence with accuracy ranging from 83 to 94 percent, depending on patient location.
The study analyzed stool samples from 674 patients enrolled in a large international clinical trial focused on high-risk melanoma cases treated with surgery and immunotherapy. Scientists identified bacterial groups such as Eubacterium, Ruminococcus, Firmicutes, and Clostridium as closely associated with recurrence risk. These microbial markers allowed researchers to distinguish between patients likely to remain cancer-free and those at higher risk of relapse.
Differences across regions initially limited the predictive power of these markers. Bacterial signatures identified in one geographic population did not always apply directly to others. To address this, the research team developed a computational method based on full DNA sequencing of gut bacteria. Instead of grouping patients by geography, they clustered them by microbiome similarity. This approach enabled a microbial signature derived from one region to accurately predict outcomes in patients from other regions, provided their microbiome profiles matched.
The analysis also showed that the gut microbiome remained stable throughout a year of immunotherapy. This stability suggests that a single test conducted before treatment could provide a reliable risk assessment. Such a test could help oncologists tailor therapies more precisely, identifying patients who may need more aggressive or alternative treatment strategies from the outset.
The clinical trial that supplied the data originally compared different immunotherapy combinations in advanced melanoma but did not show improved relapse-free survival with combined drugs. However, its large and diverse patient population created a valuable dataset for microbiome research. These new findings build on earlier evidence linking gut bacteria to immunotherapy outcomes, including studies showing that certain microbes can enhance immune response against tumors.
Future work will focus on validating this microbiome-based prediction model across other cancer types and expanding global databases to support clinical use. Researchers aim to develop a system where a patient’s microbiome is analyzed before treatment, compared against international data, and used to generate a precise prognosis that informs therapy decisions.
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