Researchers investigated the association between different types of microbes normally found in the mouth and the risk of head and neck squamous cell cancer.
The human body is colonized by trillions of microbes (bacteria, fungi, and viruses) living on and in the body. These microbes outnumber human cells by about ten to one. They are mostly found in the gut, particularly the large intestine, but they are also found in the mouth. All the genetic material contained in these microbes is called the “microbiome” and this varies between individuals. It is beginning to be understood that the pattern of the microbiome is important for health, in particular for immunity and nutrition. There has been much research looking at the associations between microbiome patterns and the risk of particular cancers.
What is the Link Between the Oral Microbiome and Head and Neck Squamous Cell Cancer?
Every year, there are over half a million new cases of head and neck cancers (mouth and throat) worldwide. About 85% of these are squamous cell cancers, meaning that they develop in the lining cells of the mouth and throat. Researchers in the US performed a large study looking at the association between oral microbiome patterns and the risk of head and neck squamous cell cancer. They recently published their findings in JAMA Oncology.
This study included 129 cases of head and neck squamous cell cancer diagnosed during two large cancer screening projects – the American Cancer Society Cancer Prevention Study (CPS-II) and the Prostate, Lung, Colorectal and Ovarian Cancer Screening Trial (PLCO) – and 254 matched control subjects from the screening studies. All subjects were cancer-free at the start of the screening period.
The CPS-II study included 184,000 participants aged between 50-74 years who completed a baseline diet and lifestyle questionnaire in 1992. The CPS-II study group sent follow up questionnaires every alternate year to update this information and to ask about any incident cancers. They -took oral wash samples from 70,000 participants in 2001-2002. The PLCO study was a large randomized study looking at the effects of screening on cancer-related mortality. This study recruited participants aged between 55-74 years between 1993 and 2001 and followed them for cancer incidence. The participants were randomized either to receive cancer screening or to the control arm (no screening). Oral wash samples were collected from those in the control arm (52,000 subjects). The follow-up included annual questionnaires to ask about incident cancers.
For the current study, the researchers analyzed the stored oral wash samples from the 129 head and neck squamous cell cancer cases and the 254 controls subjects in the laboratory to determine and compare their oral microbiome patterns.
The Overall Microbiome was not Associated with Squamous Cell Cancer
They found that the patients with head and neck cancer were more often smokers and had a greater consumption of alcohol than the control group. The overall microbiome pattern was not found to be associated with risk of head and neck squamous cell cancer. However, a greater presence of two bacteria – Corynebacterium and Kingella – was associated with a decreased risk of head and neck squamous cell cancer. These associations were particularly strong in those with a history of smoking.  Corynebacterium and Kingella are known to break down the carcinogens found in cigarette smoke, and this may be an explanation for their protective effect.
The maintenance of a healthy oral microbiome is important for oral health. The finding that an increased presence of Corynebacterium and Kingella is associated with a decreased risk of head and neck squamous cell cancer may have future implications for its prevention, in addition to measures such as stopping smoking and decreasing alcohol consumption.
Written by Julie McShane, Medical Writer
Reference: Hayes R, Ahn J, Fan X, et al. Association of oral microbiome with risk for incident head and neck squamous cell cancer. JAMA Oncology Jan 11, 2018. DOI: 10.1001/jamaoncol.2017.4777
