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Gut Microbiota in Breast Cancer Patients Differs From That of Colon Cancer Patients and Healthy Individuals: A Gut-Tumor Axis

Background: The gut microbiota influences human health and disease. Alterations in gut microbiota may have pathological consequences. Scientific knowledge about gut microbiota can facilitate predicting the likelihood of certain intestinal and/or extra-intestinal diseases. There are six main phyla in gut including Bacteroidetes, Firmicutes, Actinobacteria, Proteobacteria, Verrucomicrobia, and Fusobacteria, among which Proteobacteria and Fusobacteria are associated with colon cancer. Association of the gut microbiota pattern with colon cancer is conceivable because of their close proximity. Accordingly, breast tissue microbiota has been associated with breast tumor. Objective: This study aimed to identify the gut microbiota pattern in breast cancer, therefore, the six phyla in fecal sample from patients with breast cancer were investigated and compared with those from healthy individuals and colon cancer patients. Methods: Real-time polymerase chain reaction (PCR) was performed on DNA extracted from fecal samples based on variable region of 16S ribosomal DNA gene of the six main phyla in the gut. Results: Bacteroidetes and Firmicutes levels in breast cancer patients were higher than those in colon cancer patients and healthy individuals. Inversely, Actinobacteria, Verrucomicrobia, Proteobacteria, and Fusobacteria levels in breast cancer were lower than those in colon cancer patients and healthy individuals. Conclusion: Taking into account the decreased level of oncogenic microbiota in fecal sample from breast cancer patients compared to the level of that from colon cancer or healthy cases as well as the presence of oncogenic microbiota in breast tumor, some bacteria may have translocated from gut to breast tissue in some circumstances which likely contribute to the breast tumorigenesis (gut-tumor axis). Migration of the bacteria from gastrointestinal tract to tumor may have occurred in a similar fashion to that of the bacteria from gastrointestinal to fetus. It is worth mentioning that tumor and fetus are immune privileged sites.