Investigation of the association between the fecal microbiota and breast cancer in postmenopausal women: A population-based case-control pilot study

We investigated whether the gut microbiota differed in 48 postmenopausal breast cancer cases, pre-treatment, versus 48 controls. Microbiota profiles in fecal DNA were determined by Illumina sequencing and taxonomy of 16S rRNA genes. Estrogens were quantified in urine. Case-control comparisons employed linear and unconditional logistic regression of microbiota a-diversity (PD_whole tree) and UniFrac analysis of ß-diversity, with two-sided statistical tests. Total estrogens correlated with a-diversity in controls (Spearman Rho=0.37, P=0.009) but not cases (Spearman Rho=0.04, P=0.77). Compared to controls, cases had statistically significantly altered microbiota composition (ß-diversity, P=0.006) and lower a-diversity (P=0.004). Adjusted for estrogens and other covariates, odds ratio of cancer was 0.50 (95% confidence interval =0.30–0.85) per a-diversity tertile. Differences in specific taxa were not statistically significant when adjusted for multiple comparisons. This pilot study shows that postmenopausal women with breast cancer have altered composition and estrogen-independent low diversity of their gut microbiota. Whether these affect breast cancer risk and prognosis is unknown.