Association of breast cancer, urinary estrogens and prostaglandin E with the IgA-stained and -unstained fecal microbiota

We investigated hormonal, gut microbial, and immunologic characteristics associated with breast cancer in postmenopausal women. Microbiota metrics employed 16S rRNA sequences (Illumina) from IgA-stained and –unstained fecal microbes. Compared to healthy controls, breast cancer cases had reduced alpha diversity and altered composition of both IgA-positive and IgA-negative microbiotas. IgA-positive Immune System Diseases metabolic pathways were increased, and both IgA-positive and IgA-negative Genetic Information Processing pathways were decreased in cases (P<0.01). Urine estrogen levels were non-significantly elevated in cases; estrogens also were directly correlated with alpha diversity of the IgA-negative microbiota of the control women (P=0.012). Urine prostaglandin E metabolite levels were not associated with alpha diversity or case status. Thus, postmenopausal breast cancer had significant, but differing, associations with both IgA-positive and IgA-negative gut microbiotas, suggesting that the gut microbiota may influence breast cancer risk not only through enterohepatic cycling of estrogens but also through other pathways.