Oral Microbiome and Cancers
The human microbiome is a collection of over a trillion specific genomes of bacteria, bacteriophages, viruses
fungi, and protozoa that normally reside in the human body. The oral microbiome consists of number of such specific organisms by way of biofilms that are present in the different parts and structures of the oral cavity. The microbiome can also change depending on various circumstances from the time one is born until death. In fact, maternal influence can also be passed on at birth.
Research has shown that alterations in the oral microbiome can lead to multiple disease states, including heart diseases, loss of pregnancy, diabetes mellitus, respiratory diseases and even cancers.
Oropharyngeal cancers have long been associated with a change in the structure and function of the oral microbiome. This is especially true of cancers that do not conform to the usual known risk factors. The major risk factors for mouth cancers are tobacco and alcohol consumption, betel quid chewing, and human papillomavirus (HPV) infection. HPV-16 infection is an established cause for the majority of oropharyngeal squamous cell carcinomas. However, there is an increasing incidence of cancers despite the absence of risk factors. This fueled the need to find other potential risk factors.
Multiple studies have established various microbes and changes in different bacteria are associated with several types of cancers in the human body. In the oral microbiome, the presence of viruses and fungi and vast groups of bacteria are observed as bacterial biofilm that coat each surface of the oral cavity, and groups inhabiting these surfaces can offer a tumor microenvironment. It has been proven that the periodontal pocket is made up of stratified squamous epithelium and is continuously undergoing epithelial proliferation, migration and ulcerations.
The underlying mechanism is understood to be an activation of carcinogens by the alteration in the function of oral microbes. Another explanation offered is that a change in the structure of the genomes in some of the oral microbiome can trigger cancer formation at various sites.
Therefore, strangely enough, not just oropharyngeal cancers, but also cancers at other sites have also been now proven to have an association with the changes in the oral microbiome. Thus, oral pathology such as periodontal disease can lead to oral, esophageal, gastric, and pancreatic cancers.
Novel biomarkers have further confirmed the association of even colorectal cancer. In fact, a recent study indicates that profiling of the oral microbiome may offer an alternative screen for detecting colorectal cancer.
The clinical significance of the association between the oral microbiome and cancer is that these bacterial groups could also be used as potential biomarkers for detecting cancer early. Additionally, constant monitoring of the culprit bacteria can be used to monitor therapy and prognosis. However, further research is warranted to see if this is also feasible in clinical settings.