Western diet influences on microbiome and carcinogenesis.

The intestinal microbiota composition and associated bioactivities are sensitive to various modifier cues such as stress, inflammation, age, life-style and nutrition, which in turn are associated with susceptibility to developing cancer. Among these modifiers, diet has been shown to influence both microbiota composition as well as being an important source of microbial-derived compounds impacting the immunological, neurological and hormonal systems. Thus, it is necessary to take a holistic view when considering effect of diet on health and diseases. In this review, we focus on the interplay between western diet, the microbiota and cancer development by dissecting key components of the diet and leveraging data from human interventions and pre-clinical studies to better understand this relationship. We highlight key progress as well as stressing limitations in this field of research.

Prevalence of genotoxic bacteria in men undergoing biopsy for prostate cancer.

BACKGROUND: New evidence suggests that bacteria-produced DNA toxins may have a role in the development or progression of prostate cancer. To determine the prevalence of these genes in a noninfection (i.e., colonized) state, we screened urine specimens in men before undergoing a biopsy for prostate cancer detection. METHODS: We developed a multiplex polymerase chain reaction using three of the most described bacterial genotoxin gene primers: Colibactin (polyketone synthase [pks] gene island: clbN and clbB), cytotoxic necrotizing factor (cnf1) toxin, and cytolethal distending toxin B (cdtB) represented gene islands. After calibration on Escherichia coli samples of known genotypes, we used a training and validation cohort. We performed multiplex testing on a training cohort of previously collected urine from 45 men undergoing prostate biopsy. For the validation cohort, we utilized baseline urine samples from a previous randomized clinical trial (n = 263) with known prostate cancer outcomes. RESULTS: The prevalence of four common bacterial genotoxin genes detected in the urine before prostate biopsy for prostate cancer is 8% (25/311). The prevalence of pks island (clbN and clbB), cnf1, and cdt toxin genes are 6.1%, 2.4%, and 1.7%, respectively. We found no association between urinary genotoxins and prostate cancer (p = 0.83). We did identify a higher proportion of low-grade cancer (92% vs. 44%) in those men positive for urinary genotoxin and higher-grade cancer in those genotoxin negative (8% vs. 56%, p = 0.001). CONCLUSIONS: The prevalence of urinary genotoxins is low and does not correspond to a prostate cancer diagnosis. The urine was taken at one point in time and does not rule out the possibility of previous exposure.

GPR109a: the missing link between microbiome and good health?

A complex partnership between the host and the vast intestinal microbial ecosystem serves numerous biological activities including nutrition, immunity, and barrier function. In this issue of Immunity, Singh et al. (2014) demonstrate that microbial-derived butyrate mediated its protective activity against inflammation and colorectal cancer through GPR109a signaling.

Skin microbiome sampling in the preterm neonate.

Despite advances in our understanding of the human microbiome, there exist significant knowledge gaps in our understanding of the skin microbiome of the preterm neonate. Herein, we describe skin microbiome sampling of six preterm neonates at multiple timepoints, and compare the skin microbiome samples to environmental (crib/isolette swabs) and negative controls. Samples of the same type (skin, crib, control) were more similar than when compared by week or by patient.

NTPDase8 protects mice from intestinal inflammation by limiting P2Y6 receptor activation: identification of a new pathway of inflammation for the potential treatment of IBD.

OBJECTIVE: Nucleotides are danger signals that activate inflammatory responses via binding P2 receptors. The nucleoside triphosphate diphosphohydrolase-8 (NTPDase8) is an ectonucleotidase that hydrolyses P2 receptor ligands. We investigated the role of NTPDase8 in intestinal inflammation. DESIGN: We generated NTPDase8-deficient (Entpd8-/-) mice to define the role of NTPDase8 in the dextran sodium sulfate (DSS) colitis model. To assess inflammation, colons were collected and analysed by histopathology, reverse transcriptase-quantitative real-time PCR (RT-qPCR) and immunohistochemistry. P2 receptor expression was analysed by RT-qPCR on primary intestinal epithelium and NTPDase8 activity by histochemistry. The role of intestinal P2Y6 receptors was assessed by bone marrow transplantation experiments and with a P2Y6 receptor antagonist. RESULTS: NTPDase8 is the dominant enzyme responsible for the hydrolysis of nucleotides in the lumen of the colon. Compared with wild-type (WT) control mice, the colon of Entpd8-/- mice treated with DSS displayed significantly more histological damage, immune cell infiltration, apoptosis and increased expression of several proinflammatory cytokines. P2Y6 was the dominant P2Y receptor expressed at the mRNA level by the colonic epithelia. Irradiated P2ry6-/- mice transplanted with WT bone marrow were fully protected from DSS-induced intestinal inflammation. In agreement, the daily intrarectal injection of a P2Y6 antagonist protected mice from DSS-induced intestinal inflammation in a dose-dependent manner. Finally, human intestinal epithelial cells express NTPDase8 and P2Y6 similarly as in mice. CONCLUSION: NTPDase8 protects the intestine from inflammation most probably by limiting the activation of P2Y6 receptors in colonic epithelial cells. This may provide a novel therapeutic strategy for the treatment of inflammatory bowel disease.

Bacterial Swarmers Enriched During Intestinal Stress Ameliorate Damage.

BACKGROUND AND AIMS: Bacterial swarming, a collective movement on a surface, has rarely been associated with human pathophysiology. This study aims to define a role for bacterial swarmers in amelioration of intestinal stress. METHODS: We developed a polymicrobial plate agar assay to detect swarming and screened mice and humans with intestinal stress and inflammation. From chemically induced colitis in mice, as well as humans with inflammatory bowel disease, we developed techniques to isolate the dominant swarmers. We developed swarm-deficient but growth and swim-competent mutant bacteria as isogenic controls. We performed bacterial reinoculation studies in mice with colitis, fecal 16S, and meta-transcriptomic analyses, as well as in vitro microbial interaction studies. RESULTS: We show that bacterial swarmers are highly predictive of intestinal stress in mice and humans. We isolated a novel Enterobacter swarming strain, SM3, from mouse feces. SM3 and other known commensal swarmers, in contrast to their mutant strains, abrogated intestinal inflammation in mice. Treatment of colitic mice with SM3, but not its mutants, enriched beneficial fecal anaerobes belonging to the family of Bacteroidales S24-7. We observed SM3 swarming associated pathways in the in vivo fecal meta-transcriptomes. In vitro growth of S24-7 was enriched in presence of SM3 or its mutants; however, because SM3, but not mutants, induced S24-7 in vivo, we concluded that swarming plays an essential role in disseminating SM3 in vivo. CONCLUSIONS: Overall, our work identified a new but counterintuitive paradigm in which intestinal stress allows for the emergence of swarming bacteria; however, these bacteria act to heal intestinal inflammation.

Neonatal Fc receptor expression in dendritic cells mediates protective immunity against colorectal cancer.

Cancers arising in mucosal tissues account for a disproportionately large fraction of malignancies. Immunoglobulin G (IgG) and the neonatal Fc receptor for IgG (FcRn) have an important function in the mucosal immune system that we have now shown extends to the induction of CD8(+) T cell-mediated antitumor immunity. We demonstrate that FcRn within dendritic cells (DCs) was critical for homeostatic activation of mucosal CD8(+) T cells that drove protection against the development of colorectal cancers and lung metastases. FcRn-mediated tumor protection was driven by DCs activation of endogenous tumor-reactive CD8(+) T cells via the cross-presentation of IgG complexed antigens (IgG IC), as well as the induction of cytotoxicity-promoting cytokine secretion, particularly interleukin-12, both of which were independently triggered by the FcRn-IgG IC interaction in murine and human DCs. FcRn thus has a primary role within mucosal tissues in activating local immune responses that are critical for priming efficient anti-tumor immunosurveillance.

The microbiome, gastrointestinal cancer, and immunotherapy.

The gastrointestinal tract greatly contributes to global cancer burden and cancer-related deaths. The microbiota represents the population of microorganisms that live in and around the body, located primarily in the gastrointestinal tract. The microbiota has been implicated in colorectal cancer development and progression, but its role in cancer therapy for the gastrointestinal tract is less defined, especially for extra-intestinal cancers. In this review, we discuss the past 5 years of research into microbial involvement in immune-related therapies for colorectal, pancreatic, hepatic, and gastric cancers, with the goal of highlighting recent advances and new areas for investigation in this field.

Effect of Routine Gastric Residual Aspiration on the Preterm Infant Fecal Microbiome.

OBJECTIVE: Enteral feeding tubes are used in neonatal intensive care units (NICUs) to assess feeding tolerance by utilizing preprandial gastric residual aspiration. This study evaluates the effect of gastric residual aspiration on the preterm infant fecal microbiome and gastrointestinal inflammation. STUDY DESIGN: Fifty-one very low birth weight (VLBW) infants (≤32 weeks' gestational age and ≤1,250 g) enrolled in a larger single-center randomized controlled trial evaluating the effects of routine and nonroutine gastric residual aspiration were selected for further analysis. Of those infants, 30 had microbiome analysis performed on stools collected at 6 weeks by sequencing the bacterial V1 to V3 variable regions of the genes encoding for 16S rRNA. In an additional 21 infants, stool samples collected at 3 and 6 weeks were analyzed for intestinal inflammation using a cytokine multiplex panel. RESULTS: Microbial communities between groups were not distinct from each other and there was no difference in intestinal inflammation between groups. Analyses using gene expression packages DESeq2 and edgeR produced statistically significant differences in several taxa, possibly indicating a more commensal intestinal microbiome in infants not undergoing gastric residual aspiration. CONCLUSION: Omission of routine gastric residual aspiration was not associated with intestinal dysbiosis or inflammation, providing additional evidence that monitors preprandial gastric residuals is unnecessary. KEY POINTS: · Omission of routine gastric residual aspiration was not associated with intestinal dysbiosis or inflammation.. · Existing literature indicates preprandial gastric aspiration does not reliably correlate with development of necrotizing enterocolitis but does correlate with delayed enteral nutrition.. · Further study is required but this data that suggest monitoring preprandial gastric residuals are unnecessary..

Increased ACE2 Levels and Mortality Risk of Patients With COVID-19 on Proton Pump Inhibitor Therapy.

INTRODUCTION: Proton pump inhibitor (PPI) use was recently reported to be associated with increased severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and worse clinical outcomes. The underlying mechanism(s) for this association are unclear. METHODS: We performed a prospective study of hospitalized coronavirus disease 2019 (COVID-19) patients and COVID-negative controls to understand how PPI use may affect angiotensin-converting enzyme 2 (ACE2) expression and stool SARS-CoV-2 RNA. Analysis of a retrospective cohort of hospitalized patients with COVID-19 from March 15, 2020 to August 15, 2020 in 6 hospitals was performed to evaluate the association of PPI use and mortality. Covariates with clinical relevance to COVID-19 outcomes were included to determine predictors of in-hospital mortality. RESULTS: Control PPI users had higher salivary ACE2 mRNA levels than nonusers, 2.39 ± 1.15 vs 1.22 ± 0.92 (P = 0.02), respectively. Salivary ACE2 levels and stool SARS-CoV-2 RNA detection rates were comparable between users and nonusers of PPI. In 694 hospitalized patients with COVID-19 (age = 58 years, 46% men, and 65% black), mortality rate in PPI users and nonusers was 30% (68/227) vs 12.1% (53/439), respectively. Predictors of mortality by logistic regression were PPI use (adjusted odds ratio [aOR] = 2.72, P < 0.001), age (aOR = 1.66 per decade, P < 0.001), race (aOR = 3.03, P = 0.002), cancer (aOR = 2.22, P = 0.008), and diabetes (aOR = 1.95, P = 0.003). The PPI-associated mortality risk was higher in black patients (aOR = 4.16, 95% confidence interval: 2.28-7.59) than others (aOR = 1.62, 95% confidence interval: 0.82-3.19, P = 0.04 for interaction). DISCUSSION: COVID-negative PPI users had higher salivary ACE2 expression. PPI use was associated with increased mortality risk in patients with COVID-19, particularly African Americans.

Avenanthramide Metabotype from Whole-Grain Oat Intake is Influenced by Faecalibacterium prausnitzii in Healthy Adults.

BACKGROUND: Oat has been widely accepted as a key food for human health. It is becoming increasingly evident that individual differences in metabolism determine how different individuals benefit from diet. Both host genetics and the gut microbiota play important roles on the metabolism and function of dietary compounds. OBJECTIVES: To investigate the mechanism of individual variations in response to whole-grain (WG) oat intake. METHODS: We used the combination of in vitro incubation assays with human gut microbiota, mouse and human S9 fractions, chemical analyses, germ-free (GF) mice, 16S rRNA sequencing, gnotobiotic techniques, and a human feeding study. RESULTS: Avenanthramides (AVAs), the signature bioactive polyphenols of WG oat, were not metabolized into their dihydro forms, dihydro-AVAs (DH-AVAs), by both human and mouse S9 fractions. DH-AVAs were detected in the colon and the distal regions but not in the proximal and middle regions of the perfused mouse intestine, and were in specific pathogen-free (SPF) mice but not in GF mice. A kinetic study of humans fed oat bran showed that DH-AVAs reached their maximal concentrations at much later time points than their corresponding AVAs (10.0-15.0 hours vs. 4.0-4.5 hours, respectively). We observed interindividual variations in the metabolism of AVAs to DH-AVAs in humans. Faecalibacterium prausnitzii was identified as the individual bacterium to metabolize AVAs to DH-AVAs by 16S rRNA sequencing analysis. Moreover, as opposed to GF mice, F. prausnitzii-monocolonized mice were able to metabolize AVAs to DH-AVAs. CONCLUSIONS: These findings demonstrate that the presence of intestinal F. prausnitzii is indispensable for proper metabolism of AVAs in both humans and mice. We propose that the abundance of F. prausnitzii can be used to subcategorize individuals into AVA metabolizers and nonmetabolizers after WG oat intake. This study was registered at clinicaltrials.gov as NCT04335435.

NLRP12 suppresses colon inflammation and tumorigenesis through the negative regulation of noncanonical NF-κB signaling.

In vitro data suggest that a subgroup of NLR proteins, including NLRP12, inhibits the transcription factor NF-κB, although physiologic and disease-relevant evidence is largely missing. Dysregulated NF-κB activity is associated with colonic inflammation and cancer, and we found Nlrp12(-/-) mice were highly susceptible to colitis and colitis-associated colon cancer. Polyps isolated from Nlrp12(-/-) mice showed elevated noncanonical NF-κB activation and increased expression of target genes that were associated with cancer, including Cxcl13 and Cxcl12. NLRP12 negatively regulated ERK and AKT signaling pathways in affected tumor tissues. Both hematopoietic- and nonhematopoietic-derived NLRP12 contributed to inflammation, but the latter dominantly contributed to tumorigenesis. The noncanonical NF-κB pathway was regulated upon degradation of TRAF3 and activation of NIK. NLRP12 interacted with both NIK and TRAF3, and Nlrp12(-/-) cells have constitutively elevated NIK, p100 processing to p52 and reduced TRAF3. Thus, NLRP12 is a checkpoint of noncanonical NF-κB, inflammation, and tumorigenesis.

The short isoform of the CEACAM1 receptor in intestinal T cells regulates mucosal immunity and homeostasis via Tfh cell induction.

Carcinoembryonic antigen cell adhesion molecule like I (CEACAM1) is expressed on activated T cells and signals through either a long (L) cytoplasmic tail containing immune receptor tyrosine based inhibitory motifs, which provide inhibitory function, or a short (S) cytoplasmic tail with an unknown role. Previous studies on peripheral T cells show that CEACAM1-L isoforms predominate with little to no detectable CEACAM1-S isoforms in mouse and human. We show here that this was not the case in tissue resident T cells of intestines and gut associated lymphoid tissues, which demonstrated predominant expression of CEACAM1-S isoforms relative to CEACAM1-L isoforms in human and mouse. This tissue resident predominance of CEACAM1-S expression was determined by the intestinal environment where it served a stimulatory function leading to the regulation of T cell subsets associated with the generation of secretory IgA immunity, the regulation of mucosal commensalism, and defense of the barrier against enteropathogens.

Baseline Gut Microbiota Composition Is Associated with Major Infections Early after Hematopoietic Cell Transplantation.

Infection is a major cause of morbidity and mortality after hematopoietic cell transplantation (HCT). Gut microbiota (GM) composition and metabolites provide colonization resistance against dominance of potential pathogens, and GM dysbiosis following HCT can be deleterious to immune reconstitution. Little is known about the composition, diversity, and evolution of GM communities in HCT patients and their association with subsequent febrile neutropenia (FN) and infection. Identification of markers before HCT that predict subsequent infection could be useful in developing individualized antimicrobial strategies. Fecal samples were collected prospectively from 33 HCT recipients at serial time points: baseline, post-conditioning regimen, neutropenia onset, FN onset (if present), and hematologic recovery. GM was assessed by 16S rRNA sequencing. FN and major infections (ie, bloodstream infection, typhlitis, invasive fungal infection, pneumonia, and Clostridium difficile enterocolitis) were identified. Significant shifts in GM composition and diversity were observed during HCT, with the largest alterations occurring after initiation of antibiotics. Loss of diversity persisted without a return to baseline at hematologic recovery. GM in patients with FN was enriched in Mogibacterium, Bacteroides fragilis, and Parabacteroides distasonis, whereas increased abundance of Prevotella, Ruminococcus, Dorea, Blautia, and Collinsella was observed in patients without fever. A baseline protective GM profile (BPGMP) was predictive of protection from major infection. The BPGMP was associated with subsequent major infections with 77% accuracy and an area under the curve of 79%, with sensitivity, specificity, and positive and negative predictive values of 0.71, 0.91, 0.77, and 0.87, respectively. Our data show that large shifts in GM composition occur early after HCT, and differences in baseline GM composition are associated with the development of subsequent major infections.

Fecal Microbial Transplantation for Diseases Beyond Recurrent Clostridium Difficile Infection.

As microbiome research has moved from associative to mechanistic studies, the activities of specific microbes and their products have been investigated in the development of inflammatory bowel diseases, cancer, metabolic syndrome, and neuropsychiatric disorders. Findings from microbiome research have already been applied to the clinic, such as in fecal microbiota transplantation for treatment of recurrent Clostridium difficile infection. We review the evidence for associations between alterations in the intestinal microbiome and gastrointestinal diseases and findings from clinical trials of fecal microbiota transplantation. We discuss opportunities for treatment of other diseases with fecal microbiota transplantation, based on findings from small clinical and preclinical studies.

Gut microbiota maturation during early human life induces enterocyte proliferation via microbial metabolites.

BACKGROUND: The intestinal tract undergoes a period of cellular maturation during early life, primarily characterized by the organization of epithelial cells into specialized crypt and villus structures. These processes are in part mediated by the acquisition of microbes. Infants delivered at term typically harbor a stable, low diversity microbiota characterized by an overrepresentation of various Bacilli spp., while pre-term infants are colonized by an assortment of bacteria during the first several weeks after delivery. However, the functional effects of these changes on intestinal epithelium homeostasis and maturation remain unclear. To study these effects, human neonate feces were obtained from term and pre-term infants. Fecal 16S rDNA sequencing and global untargeted LC-MS were performed to characterize microbial composition and metabolites from each population. Murine enteral organoids (enteroids) were cultured with 0.22 µm filtered stool supernatant pooled from term or pre-term infants. RESULTS: Term and pre-term microbial communities differed significantly from each other by principle components analysis (PCoA, PERMANOVA p < 0.001), with the pre-term microbiome characterized by increased OTU diversity (Wilcox test p < 0.01). Term communities were less diverse and dominated by Bacilli (81.54%). Pre-term stools had an increased abundance of vitamins, amino acid derivatives and unconjugated bile acids. Pathway analysis revealed a significant increase in multiple metabolic pathways in pre-term samples mapped to E. coli using the KEGG database related to the fermentation of various amino acids and vitamin biosynthesis. Enteroids cultured with supernatant from pre-term stools proliferated at a higher rate than those cultured with supernatant from term stools (cell viability: 207% vs. 147.7%, p < 0.01), grew larger (area: 81,189µm2 vs. 41,777µm2, p < 0.001), and bud at a higher rate (6.5 vs. 4, p < 0.01). Additionally, genes involved in stem cell proliferation were upregulated in pre-term stool treated enteroid cultures (Lgr5, Ephb2, Ascl2 Sox9) but not term stool treated enteroids. CONCLUSIONS: Our findings indicate that microbial metabolites from the more diverse gut microbiome associated with pre-term infants facilitate stem cell proliferation. Therefore, perturbations of the pre-term microbiota may impair intestinal homeostasis.

Protective mucosal immunity mediated by epithelial CD1d and IL-10.

The mechanisms by which mucosal homeostasis is maintained are of central importance to inflammatory bowel disease. Critical to these processes is the intestinal epithelial cell (IEC), which regulates immune responses at the interface between the commensal microbiota and the host. CD1d presents self and microbial lipid antigens to natural killer T (NKT) cells, which are involved in the pathogenesis of colitis in animal models and human inflammatory bowel disease. As CD1d crosslinking on model IECs results in the production of the important regulatory cytokine interleukin (IL)-10 (ref. 9), decreased epithelial CD1d expression--as observed in inflammatory bowel disease--may contribute substantially to intestinal inflammation. Here we show in mice that whereas bone-marrow-derived CD1d signals contribute to NKT-cell-mediated intestinal inflammation, engagement of epithelial CD1d elicits protective effects through the activation of STAT3 and STAT3-dependent transcription of IL-10, heat shock protein 110 (HSP110; also known as HSP105), and CD1d itself. All of these epithelial elements are critically involved in controlling CD1d-mediated intestinal inflammation. This is demonstrated by severe NKT-cell-mediated colitis upon IEC-specific deletion of IL-10, CD1d, and its critical regulator microsomal triglyceride transfer protein (MTP), as well as deletion of HSP110 in the radioresistant compartment. Our studies thus uncover a novel pathway of IEC-dependent regulation of mucosal homeostasis and highlight a critical role of IL-10 in the intestinal epithelium, with broad implications for diseases such as inflammatory bowel disease.

Campylobacter jejuni promotes colorectal tumorigenesis through the action of cytolethal distending toxin.

OBJECTIVE: Campylobacter jejuni produces a genotoxin, cytolethal distending toxin (CDT), which has DNAse activity and causes DNA double-strand breaks. Although C. jejuni infection has been shown to promote intestinal inflammation, the impact of this bacterium on carcinogenesis has never been examined. DESIGN: Germ-free (GF) ApcMin/+ mice, fed with 1% dextran sulfate sodium, were used to test tumorigenesis potential of CDT-producing C. jejuni. Cells and enteroids were exposed to bacterial lysates to determine DNA damage capacity via γH2AX immunofluorescence, comet assay and cell cycle assay. To examine the interplay of CDT-producing C. jejuni, gut microbiome and host in tumorigenesis, colonic RNA-sequencing and faecal 16S rDNA sequencing were performed. Rapamycin was administrated to investigate the prevention of CDT-producing C. jejuni-induced tumorigenesis. RESULTS: GF ApcMin/+ mice colonised with human clinical isolate C. jejuni81-176 developed significantly more and larger tumours when compared with uninfected mice. C. jejuni with a mutated cdtB subunit, mutcdtB, attenuated C. jejuni-induced tumorigenesis in vivo and decreased DNA damage response in cells and enteroids. C. jejuni infection induced expression of hundreds of colonic genes, with 22 genes dependent on the presence of cdtB. The C. jejuni-infected group had a significantly different microbial gene expression profile compared with the mutcdtB group as shown by metatranscriptomic data, and different microbial communities as measured by 16S rDNA sequencing. Finally, rapamycin could diminish the tumorigenic capability of C. jejuni. CONCLUSION: Human clinical isolate C. jejuni 81-176 promotes colorectal cancer and induces changes in microbial composition and transcriptomic responses, a process dependent on CDT production.

International Cancer Microbiome Consortium consensus statement on the role of the human microbiome in carcinogenesis.

OBJECTIVE: In this consensus statement, an international panel of experts deliver their opinions on key questions regarding the contribution of the human microbiome to carcinogenesis. DESIGN: International experts in oncology and/or microbiome research were approached by personal communication to form a panel. A structured, iterative, methodology based around a 1-day roundtable discussion was employed to derive expert consensus on key questions in microbiome-oncology research. RESULTS: Some 18 experts convened for the roundtable discussion and five key questions were identified regarding: (1) the relevance of dysbiosis/an altered gut microbiome to carcinogenesis; (2) potential mechanisms of microbiota-induced carcinogenesis; (3) conceptual frameworks describing how the human microbiome may drive carcinogenesis; (4) causation versus association; and (5) future directions for research in the field.The panel considered that, despite mechanistic and supporting evidence from animal and human studies, there is currently no direct evidence that the human commensal microbiome is a key determinant in the aetiopathogenesis of cancer. The panel cited the lack of large longitudinal, cohort studies as a principal deciding factor and agreed that this should be a future research priority. However, while acknowledging gaps in the evidence, expert opinion was that the microbiome, alongside environmental factors and an epigenetically/genetically vulnerable host, represents one apex of a tripartite, multidirectional interactome that drives carcinogenesis. CONCLUSION: Data from longitudinal cohort studies are needed to confirm the role of the human microbiome as a key driver in the aetiopathogenesis of cancer.