**5. Clinical applications of microbiome analysis**

Some studies stablish a relationship between the microbiota and the cancer therapy efficacy. Iida et al. showed that microbiota leads to enzyme expression required for optimal chemotherapy activity with oxaliplatin [18]. Guthrie et al. demonstrated that inhibition of microbial ß-glucuronidase increases the adverse effects of irinotecan in some patients [33]. Concerning immunotherapy, a great number of bacteria were observed having great clinical response to immunecheckpoint therapy (by activating CTLA-4 and PD1 expression or promoting T-cell proliferation) [34].

Nevertheless, the main application nowadays is the fecal microbiota transplantation. This procedure consists in the administration of fecal bacteria from a healthy donor (without cancer, an autoimmune or metabolic disease) to a recipient by enema, colonoscopy, or enteric tube. The main objective is to alter the recipient's microbiota composition, and it is performed in a variety of diseases like *Clostridium difficile* infection, irritable bowel syndrome, inflammatory bowel diseases, obesity, multiple sclerosis, and type 2 diabetes mellitus [35]. Unfortunately, the lack of evidence and clinical trials bounds their use in clinical practice of oncologic patients.

Another potential application is through oral probiotics. Probiotics are supplements with live bacteria that promote gut health. Some experimental models presented a reduction rate of colorectal cancer development with their consumption [36].
