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The bacteria that inhabit our gut – the gut microbiome - could have profound impact on our health. The species that live in our guts influence the development of neurodegenerative disease (Alzheimer disease, Parkinson’s disease), epilepsy, autoimmune disease, and cancer.4 They may also be helping shape whether our treatments work.

Hundreds of trillions of microbes reside in our gastrointestinal tract, primarily in the colon 1. The bacterial genomes contain 3.3 million active genes which is 150 times the size of the human genome (22,000 genes) 2. Advances in sequencing technology allows researchers to study the genetics of the microbial community quickly and cheaply. One of the most well-known examples is The Human Microbiome Project.3

In cancer research, Helicobacter pylori is the most famous and earliest defined link between bacteria and cancer 5. More recently, dysbiosis is linked to colorectal cancer.6. Atopobium parvulum and Actinomyces odontolyticus were enriched in multiple polypoid adenomas and intramucosal carcinomas, and Fusobacterium nucleatum numbers increased during progression from intramucosal carcinoma to more advanced stages of the disease.

In cancer treatment, the gut microbiome is important during treatment with immunotherapies, such as CTLA-47, PD-L1 checkpoint blockade8 and CpG-oligonucleotide treatment9.  We also know that using faecal microbiota transplantation, helped boost the immune system response in immunotherapy and in chemotherapy. 10.11

We are beginning to understand how the gut biome connects with the immune system. One Japanese group identified a collection of 11 strains of gut bacteria that have a significant and positive effect on the work of immune cells like CD8 T-cells12 and others have shown that the right gut biome can boost cytotoxic T cells.13 Like the gut-brain-axis that connects the gut microbiota with the central nervous system, immunity is the well-accepted cross talk between gut microbiota and anti-cancer treatment.

In addition, to the gut biome itself, microbial metabolites likes short chain fatty acids, phenolic acids and isothiocyanates provide other anti-carcinogenic mechanisms 14. Interestingly, short-chain fatty acid – butyrate has been shown to accumulate in cancerous cell due to the Warburg effect15 and an increased uptake of acetate has been observed in hypoxic cancer cells. These metabolites cause stress in cancer cells, which may make them more susceptible to our therapies.

There is much exciting news from studying the gut microbiota in cancer research, although there is still a long way to go in studying the role of the gut microbiota to cancer/anti-cancer treatment. The role of HPV in cervical cancer is well known. Who knows what other virome16, yeast, fungus and archaea 17 besides gut bacteria may help us fight cancer. It may be that your gut is more important than you thought! 


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  2. Qin, J. et al. A human gut microbial gene catalogue established by metagenomic sequencing. Nature 464, 59-65, doi:10.1038/nature08821 (2010).
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