The landscape of the intestinal microbiome among patients with newly diagnosed invasive breast cancer and ductal carcinoma in situ (DCIS).

The intestinal microbiome shapes immune responses and is associated with patient outcomes in cancer following immunotherapy. We evaluated differences between the intestinal microbiome profiles of patients with early-stage invasive breast cancer (BC) and ductal carcinoma in situ (DCIS) by subtype using whole genome metagenomic sequencing. There were no significant differences in microbiome composition between DCIS and invasive BC as measured by alpha diversity (p = 0.20, ANOVA) or beta diversity (p = 0.52, PERMANOVA). Within invasive BC, patients with hormone receptor-positive (HR + )/HER2 + BC differed significantly in beta diversity relative to other subtypes (p < 0.05), with differences in six species (q < 0.25). Bacteroides ovatus was significantly more abundant in patients with stage III BC vs. stage I (p = 0.0003). Functional pathway analysis using HUMAnN3 revealed stage-specific enrichment of amino acid biosynthesis and nucleotide-related pathways. Altogether, these findings highlight potential microbial signatures associated with BC subtype and stage.