The 2026 ESCMID Global Congress underscored a critical shift in oncology: the microbiome's function, not just its composition, is a key determinant of cancer therapy response. New data shows that microbial metabolic activity can significantly influence outcomes for patients on immunotherapy and chemotherapy.
Microbiome & Immunotherapy
Strong evidence links gut microbiome profiles to immune checkpoint inhibitor efficacy. Facal microbiota transplantation (FMT) from responders has shown clinical benefit in refractory melanoma patients, supporting a causal relationship. The effect appears driven by broader ecosystem characteristics rather than single bacteria.
Antibiotics & Treatment Disruption
Antibiotic use, common in cancer patients, is consistently linked to worse immunotherapy outcomes. Meta-analyses of over 46,000 patients confirm that broad-spectrum antibiotics disrupt microbial diversity, impairing treatment response. This highlights the urgent need for careful antibiotic stewardship.
Beyond Composition: The Rise of Microbial Function
A key theme was the move from taxonomy to function. Studies on prebiotics like camu camu showed improved clinical outcomes with minimal compositional changes but significant shifts in metabolomic profiles. Key pathways identified include bile acid and tryptophan metabolism.
Microbiome & Chemotherapy
The microbiome also affects chemotherapy efficacy and toxicity. In pancreatic cancer, intratumoral bacteria can inactivate gemcitabine, leading to resistance. This effect is drug-specific and is being targeted in clinical trials like PRODIGE 106 PANORAMIX.
Therapeutic Modulation
FMT trials, including FMT-LUMinate and TACITO, reported encouraging response rates in melanoma, lung, and renal cell cancers. Notably, common probiotics may impair recovery. New microbiome-sparing antibiotics like lolamicin show promise by preserving microbial diversity.
Expert Perspective
The field is converging on a function-oriented approach. There is no single 'healthy' microbiome; rather, identifying functional profiles and harmful microbial patterns is key to developing broadly applicable, microbiome-based strategies for cancer care.