Researchers have known for decades that the bacteria harbored in our bodies are not innocent bystanders but rather active participants in health and disease. Yet only recently have molecular methods evolved to the point that they can identify and characterize some of our microbial residents.
While cancer-associated bacteria have long been considered to be opportunistic (i.e., infecting healthy tissues after cancer has already established itself), there is some evidence that bacteria may be directly carcinogenic.
The strongest evidence to date involves the bacterium H. pylori and its role in gastric cancer. Understanding cancer’s relationship with the human microbiome could transform immune-modulating therapies.
The most logical link between the microbiome and cancer is our immune system. Resident microbes can either increase inflammation or reduce the effect, and can regulate immune cells sensitivity to invaders. Not only does the immune system appear to play an active part of how the microbiome interacts with cancer therapies, it also appears to mediate how our bacteria, fungi, and viruses influence cancer development in the first place.