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The type and frequency of bacteria found in the mouth may be related to the risk of lung cancer in non-smokers. This is evident from the first study of its kind published online in the journal Thorax.
Fewer types and high numbers of certain types of bacteria appear to be associated with an increased risk.
About one in four cases of lung cancer occurs in nonsmokers, and known risk factors such as second-hand tobacco smoke, background radon exposure, air pollution, and family history of lung cancer don’t fully explain these numbers, the researchers say.
The type and volume of bacteria (microbiomes) in the mouth have been linked to an increased risk of various types of cancer, including those of the esophagus, head and neck, and pancreas.
And the researchers wanted to find out whether this connection also applies to lung cancer, since the mouth is the entry point for bacteria into the lungs.
They relied on participants in the Shanghai Women’s Health Study and Shanghai Men’s Health Study, who were all non-smokers for life and whose health was monitored every 2-3 years after entering the study between 1996 and 2006.
Upon enrollment, participants rinsed their mouths to get a profile of the resident bacteria and obtained information on lifestyle, diet, medical history, and other environmental and workplace factors that could influence disease risk.
A total of 90 of the women and 24 of the men developed lung cancer within an average of 7 years.
These cases were compared to 114 non-smokers of the same age and sex who also provided a mouthwash sample. This comparison group did not have lung cancer, but they had a similar educational level and family history of lung cancer.
A comparison of both sets of lavage samples showed that the microbiome differed between the two groups. A wider range of types of bacteria were associated with a lower risk of developing lung cancer. A greater volume of certain species was also linked to the risk of lung cancer.
A larger volume of Bacteroidetes and Spirochaetes species was associated with a lower risk, while a larger volume of Firmicutes species was associated with an increased risk.
Within the Spirochaetes species in particular, a higher frequency of Spirochaetia was associated with a lower risk; and within the Firmicutes species, a greater volume of organisms from the Lactobacillales order of microbes was associated with an increased risk.
The associations persisted when the analysis was limited to those participants who had not taken antibiotics in the 7 days prior to specimen collection and after excluding those diagnosed with lung cancer within 2 years of specimen collection.
This is an observational study and therefore cannot determine a cause. And the researchers recognize several limitations. “While our study provides evidence that variations in the oral microbiome play a role in lung cancer risk, the interpretation of our study must be made with the caveat that our results come from a single point in time in a single geographic location,” they write.
In a linked editorial, Dr. David Christiani of Harvard University suggests that oral bacteria can cause chronic inflammation, promote cell proliferation and inhibit cell death, trigger DNA changes and turn on cancer genes and their blood supply, which would help explain the results.
The study results raise several questions, he says. “First, how stable is the human oral microbiome over time? Second, if the human oral microbiome changes over time, what determines this variability? Third, how does the environment such as exposure to air pollutants affect the mouth (and the Lungs). Microbiome? “
He adds, “It remains unclear whether the oral microbiome measured in this (and other) epidemiological studies is a pathogen or just a marker of disease or immune activity. If it is, it is important to understand whether the oral microbiome is actually sows the lung microbiome and thus acts locally. ”
The lung microbiome can influence the pathogenesis and prognosis of lung cancer
Oral microbiome variation has been linked to future lung cancer risk in nonsmokers, Thorax (2020). DOI: 10.1136 / thoraxjnl-2020-215542
Editorial: Oral Microbiome and Lung Cancer Risk, Thorax (2020). DOI: 10.1136 / thoraxjnl-2020-216385
Supplied by the British Medical Journal
Quote: Type and frequency of oral bacteria in relation to the risk of lung cancer in non-smokers (2020, December 14th), accessed December 15, 2020 from https://medicalxpress.com/news/2020-12-abundance-mouth-bacteria-linked- lung .html
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