L26/P-370 Molecular and Microbial Alterations in Eutopic Endometrium of Endometriosis Patients: Insights into a Biologically Hostile Environment

Abstract Study question Do specific molecular markers or the endometrial microbiome exhibit alterations in the eutopic endometrium of patients with endometriosis? Summary answer Eutopic endometrium in endometriosis displays a set of molecular and microbial alterations, reflecting a biologically challenging environment that calls for integrated multi-marker assessment. What is known already Eutopic endometrium in endometriosis may harbor functional defects, yet the evidence is conflicting, particularly regarding apoptotic resistance (e.g., BCL6 overexpression). The “pathogens colonization hypothesis” proposes that microorganisms such as Fusobacterium promote local inflammation, contributing to pathogenesis. Integrated analyses combining metabolic and oxidative stress markers, apoptotic pathways, and microbiome profiling remain limited. Determining whether these alterations are intrinsic, genetically determined, or acquired due to a hostile microenvironment is critical for developing personalized infertility management strategies. Study design, size, duration This retrospective/prospective observational study analyzed 580 endometrial samples from patients undergoing endometrial testing due to previous reproductive failure, single-embryo availability, or patient request.The cohort included 392 Controls (indication: one embryo available) and 188 Endometriosis patients (mean age: 40.8 vs 38.6 years). A sub-cohort of 78 patients (35 Controls, 43 Endometriosis, mean age= 39.7 vs 38 years) underwent targeted gene expression analysis to explore apoptotic and receptivity-related molecular signatures. Participants/materials, setting, methods Endometrial biopsies were obtained during the implantation window. Receptivity was assessed using a validated 48-gene microfluidic algorithm. Microbiome profiling employed an RT-qPCR panel targeting bacteria, viruses, fungi, and protozoa associated with reproductive success. The sub-cohort (n = 78) was prospective analyzed for apoptotic and receptivity-related gene expression by RT-qPCR. Statistical comparisons used Wilcoxon signed ranks and Fisher’s exact tests. Main results and the role of chance Targeted transcriptomic profiling revealed a distinct molecular signature in endometriosis patients. Classical apoptotic regulators were largely unchanged (p > 0.05), though BCL6 showed the largest fold change (Log2FC -2.13), reflecting inter-patient heterogeneity. MAOA was significantly upregulated (p < 0.01) and HBA1 downregulated (p < 0.05), possibly consistent with oxidative stress and metabolic dysregulation. Despite these molecular deviations, global markers of endometrial receptivity, including receptivity classification, remained comparable between groups (p > 0.05). Microbiome analysis revealed quantitative alteration in endometriosis patients, with significantly higher pathogen load (p < 0.0001) and increased Candida levels (p < 0.001), along with reduced Lactoferrin, indicating compromised local immune defense. Other pathogens showed a non-significant trend toward increase. These microbial alterations paralleled molecular stress signatures, suggesting interplay between microbial imbalance, oxidative stress, and metabolic dysregulation. Together, these findings delineate a complex phenotype in which the eutopic endometrium in endometriosis retains temporal and functional receptivity, yet exists within a biologically stressed microenvironment characterized by increased pathogenic load, fungal overrepresentation, and impaired local immune defense. This dichotomy underscores the necessity of integrating molecular and microbial profiling to comprehensively assess reproductive competence in endometriosis, emphasizing that normal receptivity markers alone may not reflect an optimal endometrial milieu. Limitations, reasons for caution The retrospective design should be considered when interpreting the findings. Sample size for transcriptomic analyses was limited, and lack of paired eutopic and ectopic tissues restricts conclusions. Prospective studies with larger cohorts are needed to confirm findings and clarify endometrial alterations in endometriosis. Wider implications of the findings These findings emphasize the value of a multi-marker evaluation approach for assessing eutopic endometrial health in endometriosis. Integrating molecular, metabolic, and microbial assessments may enable more personalized therapies, optimize infertility management, and enhance endometriosis diagnosis and treatment strategies beyond conventional evaluation. Trial registration number No