Gut microbiome and its association with sociodemographic and clinical characteristics in Peruvian women with breast cancer: results of a multicenter study

Introduction: Breast cancer is the most common cancer in women worldwide and a leading cause of cancer-related death. Emerging evidence suggests that the gut microbiota may influence biological processes involved in breast carcinogenesis. However, Latin American populations, with their high genetic, environmental, and dietary diversity, remain underrepresented in this field. Objective : To characterize the composition and diversity of the gut microbiota in Peruvian women with breast cancer treated at three oncology institutions in different geographic regions of Perú, and to evaluate its variation according to geographic origin, clinical stage, and molecular subtype. Materials and methods: A multicenter cross-sectional analytical observational study was conducted in 77 patients between 2023 and 2024. Clinical data and fecal samples were collected; the V3–V4 region of the 16S rRNA gene was sequenced and reads were resolved into amplicon sequence variants (ASVs). Alpha diversity (observed richness, Shannon index), beta diversity (Bray-Curtis dissimilarity and principal coordinates analysis [PCoA]), and relative abundance of taxa were assessed. Comparisons were performed using Kruskal-Wallis, Wilcoxon, and PERMANOVA tests. Results: The sample presented a common microbial core dominated by Faecalibacterium, Segatella , Blautia , Vescimonas and Bacteroides . Alpha diversity did not differ significantly among the three cities. Overall community structure did not differ significantly by region (PERMANOVA, Bray–Curtis R² = 0.036, p = 0.109), clinical stage (p = 0.23) or molecular subtype (p = 0.20); Pairwise comparisons suggested a nominal difference between Trujillo and Arequipa (R² = 0.037, p = 0.019), although this association did not remain significant after Firmicutes/Bacteroidota ratio correction (adjusted p = 0.057). The F/B ratio differed significantly by region (Kruskal–Wallis p = 0.012), being highest in Trujillo and lowest in Arequipa (adjusted p = 0.02). No bacterial genus remained significantly associated with any geographic or clinical variable after correction for multiple testing. Conclusions : Peruvian women with breast cancer exhibit a relatively stable gut microbial community whose overall structure is not significantly associated with geographic origin, clinical stage, or molecular subtype. Nevertheless, regional differences were observed in the Firmicutes/Bacteroidota ratio, suggesting modest geographic variation in microbiota composition.