Microbiota composition in bilateral healthy breast tissue and breast tumors.

[PURPOSE] Previous reports suggest that a complex microbiome exists within the female human breast that might contribute to breast cancer etiology. The purpose of this pilot study was to assess the variation in microbiota composition by breast side (left versus right) within individual women and compare the microbiota of normal and breast tumor tissue between women. We aimed to determine whether microbiota composition differs between these groups and whether certain bacterial taxa may be associated with breast tumors.

[METHODS] Bilateral normal breast tissue samples (n = 36) were collected from ten women who received routine mammoplasty procedures. Archived breast tumor samples (n = 10) were obtained from a biorepository. DNA was extracted, amplified, and sequenced. Microbiota data were analyzed using QIIME and RStudio.

[RESULTS] The most abundant phyla in both tumor and normal tissues were Bacteroidetes, Firmicutes, Proteobacteria, and Actinobacteria. There were statistically significant differences in the relative abundance of various bacterial taxa between groups. Alpha diversity (Simpson's index) was significantly higher in normal compared to tumor samples (0.968 vs. 0.957, p = 0.022). Based on unweighted UniFrac measures, breast tumor samples clustered distinctly from normal samples (R = 0.130; p = 0.01). Microbiota composition in normal samples clustered within women (R = 0.394; p = 0.01) and by breast side (left or right) within a woman (R = 0.189; p = 0.03).

[CONCLUSION] Significant differences in diversity between tumor and normal tissue and in composition between women and between breasts of the same woman were identified. These results warrant further research to investigate the relationship between microbiota and breast cancer.