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Study co-corresponding author Maria Rescigno

Credit: ÖAW/Natascha Unkart

The tumor microbiota — encompassing bacteria, fungi, viruses, and other microorganisms found within tumor tissue — is increasingly recognized as a key element of the tumor microenvironment. An international consensus paper published in Cancer Cell brings together leading institutions from the United States, Israel, Austria, and Italy that are advancing research in this rapidly evolving field. Among the co-corresponding authors is Maria Rescigno, Scientific Director of the CeMM Research Center for Molecular Medicine of the Austrian Academy of Sciences, Professor of General Pathology at Humanitas University, and Head of the Laboratory of Mucosal Immunology and Microbiota at IRCCS Istituto Clinico Humanitas. Luca Tiraboschi, a researcher in the same laboratory, is also a co-author. Together with an international consortium, the team reviewed current evidence, outlined major methodological obstacles, and proposed shared standards to enable more accurate and reproducible identification of microbes associated with tumors.

Microbes and tumors: a complex relationship

Over the past decade, findings from preclinical models and clinical studies have shown that the gut microbiota plays a significant role in cancer progression and in shaping responses to immunotherapy. International research efforts have demonstrated that altering microbial communities can influence not only tumors of the intestine but also cancers arising in distant organs, including the brain, liver, pancreas, breast, bone, and skin. Microbial signals — and in some instances living microorganisms — have been detected within tumor tissues, where they can reshape both cancer cells and immune cell behavior. “These findings indicate that microbes associated with tumors are not passive bystanders, but active regulators of tumor biology and therapeutic outcomes. However, studying them rigorously is challenging because they are often present in very low quantities, are susceptible to contamination, and can be affected by methodological biases. Clarifying their role will be crucial for designing more precise therapeutic strategies,” explains Maria Rescigno.

Toward more precise therapies

Scientists have identified several mechanisms by which microbes may influence tumor development. Structural components such as fragments of microbial cell walls and nucleic acids, along with metabolites produced by microbes, can circulate through the body and reach tumors, where they reshape the local microenvironment and directly influence cellular and immune pathways. In certain situations, viable microorganisms can migrate from the gut or other mucosal surfaces into tumor tissue, establishing direct interactions that affect local immune responses.

This body of evidence has led to a clearer definition of the tumor microbiota as the collection of microorganisms and their molecular products — including nucleic acids, proteins, and metabolites — that are present within tumor tissue and its surrounding ecological niche. This definition distinguishes them from microbial communities that reside only on organ surfaces or within cavities and do not penetrate tumor tissue, while emphasizing their potential to interact with host cells.

To overcome technical limitations and reduce the risk of misinterpretation, the consensus paper recommends combining multiple complementary techniques, including genetic sequencing, imaging technologies, microbial culture methods, and functional assays. Such integration is necessary to confirm not only the presence of microbial material but also microbial viability and causal involvement in tumor processes. The authors further propose minimum reporting criteria to promote consistency and reproducibility across laboratories. “The aim is to move beyond the simple question of whether microbes are present and instead address clinically meaningful issues: how tumor-associated microbes shape tumor biology and influence treatment responses, and whether they can serve as biomarkers to guide more personalized and effective therapies,” adds Luca Tiraboschi.

Clinical implications and future perspectives

A deeper understanding of the tumor microbiota offers promising new avenues for cancer treatment. As has already been demonstrated for the gut microbiota, strategies that target microbes within tumors could potentially enhance the efficacy of immunotherapy, chemotherapy, and other anticancer approaches. Identifying clear causal mechanisms will be essential to translate these discoveries into practical precision oncology applications.

This study represents a major collaborative effort at the international level and integrates findings across multiple tumor types, particularly those characterized by low microbial biomass, where especially rigorous validation is required. By establishing a framework of experimental and analytical standards, the work lays the groundwork for more robust investigations and future clinical advances in the emerging field of tumor microbiota research.

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The study “Toward a Consensus on the Tumor Microbiota: Evidence, Standards, and Interpretation” was published in Cancer Cell on 12 March 2026.

Authors: Tingting Duan, Aviel Rosenbaum, Vidhi Chandra, Luca Tiraboschi, Maria Rescigno#, Florencia McAllister#, Ravid Straussman#, Marlies Meisel# (#shared corresponding authors)

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The CeMM Research Center for Molecular Medicine of the Austrian Academy of Sciences is an independent and interdisciplinary institute dedicated to advancing molecular medicine under the scientific leadership of Maria Rescigno. The center focuses on addressing pressing medical needs by integrating basic scientific research with clinical expertise to develop innovative diagnostic and therapeutic strategies in precision medicine. Its research areas include cancer, inflammatory conditions, metabolic and immune disorders, and rare diseases. The institute is located on the campus of the Medical University and the Vienna General Hospital.

Journal

Cancer Cell

DOI

10.1016/j.ccell.2026.02.011

Method of Research

Literature review

Subject of Research

Cells

Article Title

Toward a Consensus on the Tumor Microbiota: Evidence, Standards, and Interpretation

Article Publication Date

12-Mar-2026