Microbial and Environmental Factors Associated With Polyps Development in Familial Adenomatous Polyposis (MicrobEnvironment in FAP)

Familial adenomatous polyposis (FAP) is a hereditary condition caused by mutations in the APC gene that inevitably leads to colorectal cancer if the colon is not surgically removed. Even among people with identical APC mutations, there is striking variation in how quickly and severely polyps develop — suggesting that external factors, including the gut microbiome, play an important modifying role. This French prospective study (MicrobEnvironment in FAP) aims to systematically characterize the gut and duodenal microbiota of FAP patients over time and link specific microbial signatures to the rate and severity of adenoma development. A key innovation is the focus on duodenal microbiota, which is underexplored relative to colonic microbiota in FAP. Researchers will also capture environmental exposures such as diet, medications, and lifestyle to build a multivariable picture of carcinogenic risk. The study is currently recruiting and expects to complete data collection by May 2026. If a reproducible microbial signature associated with faster polyp progression is identified, it could eventually inform surveillance strategies or microbiome-targeted prevention trials.

• Study is actively recruiting (as of 2024); no efficacy or association results are yet available — all findings below are protocol-level design features reported in the registration.
• The protocol identifies gut microbiota as a hypothesized co-factor in FAP carcinogenesis, with the primary aim of defining a microbiological signature linked to adenoma incidence and severity at both colonic and duodenal sites.
• Inter- and intra-familial variability in polyp development for identical APC mutations is cited as key motivation, implying that non-genetic (environmental and microbial) factors account for a clinically meaningful proportion of phenotypic variance.

This is a prospective longitudinal observational cohort study recruiting FAP patients at Hospices Civils de Lyon, France, with an anticipated completion date of May 2026. Participants undergo scheduled endoscopic surveillance (colonoscopy and upper GI endoscopy), at which point mucosal and luminal samples are collected for microbiome profiling at both colonic and duodenal levels. Environmental data — including diet, antibiotic use, NSAIDs, and lifestyle factors — are collected in parallel to enable multivariable modelling. Sample size and full inclusion/exclusion criteria were not disclosed in the available abstract extract (best-effort assessment from registry metadata).

Because this is an observational cohort study, it cannot establish causality between any microbial signature and adenoma progression — only association. The study does not appear to include a non-FAP control arm, which limits ability to distinguish FAP-specific dysbiosis from background variation. Duodenal microbiota sampling is technically challenging and subject to contamination from the upper GI tract, potentially affecting reproducibility. The next critical experiment would be an intervention trial (e.g., probiotic, prebiotic, or fecal microbiota transplant) in FAP patients stratified by the microbial signatures identified here, to test whether modifying the microbiome alters adenoma burden.

This study extends the mechanistic framework developed in [§139], which demonstrates that gut microbiota dysbiosis can remodel multi-tissue transcriptional landscapes, by asking whether such dysbiosis has a measurable impact on adenoma progression in a genetically defined high-risk population. It parallels [§73], which investigates the bile acid/gut microbiome axis as a mechanism linking diet to colorectal cancer risk — an axis highly relevant to FAP given the duodenal focus of the present study. The longitudinal design also parallels [§102] (Westlake Frequent-sampling Cohort), which demonstrates how repeated within-individual sampling can resolve microbiome dynamics that cross-sectional studies miss. If a pathogenic microbial signature is confirmed, the study would provide the ecological rationale needed to justify microbiome-modulating interventions, situating it upstream of emerging dietary and probiotic RCTs such as [§100], which frames the microbiome as a causal rather than merely correlative contributor to disease.

• Mediterranean Diet and Weight Loss: Targeting the Bile Acid/Gut Microbiome Axis to Reduce Colorectal Cancer
  Directly relevant comparator: investigates the bile acid/gut microbiome axis and Mediterranean diet as modulators of colorectal cancer risk — the same mechanistic pathway implicated in FAP carcinogenesis, but in a non-hereditary CRC population, allowing readers to assess how genetic predisposition modifies microbiome effects.
• Gut Microbiota Dysbiosis Remodels the Multi-Tissue Transcriptional Landscape of the Host
  Provides mechanistic depth: demonstrates that microbiota dysbiosis remodels host transcriptional programs across multiple tissues, supporting the biological plausibility of the MicrobEnvironment in FAP hypothesis that microbial shifts drive adenoma progression beyond the APC mutation alone.
• The human microbiome at translational crossroads: an ecological and causal perspective
  Methodological and conceptual anchor: argues for moving from ecological correlation to causal inference in microbiome research — directly relevant to evaluating what this FAP observational cohort can and cannot conclude, and what intervention design would logically follow.
• Westlake Frequent-sampling Cohort 2
  Design comparator: the Westlake Frequent-sampling Cohort demonstrates the analytical advantages of dense longitudinal sampling for capturing microbiome dynamics, offering a methodological benchmark for the FAP cohort's repeated endoscopic sampling strategy.
• Enterotype-specific microbial biomarkers of immune checkpoint inhibitor response revealed by large-scale integrated metagenomic analysis
  Parallel translational model: shows that enterotype-specific microbial biomarkers can predict clinical outcomes (immunotherapy response) — illustrating the broader principle that microbiome signatures can stratify patient risk, which is precisely what MicrobEnvironment in FAP aims to achieve for adenoma progression.