Type, abundance of oral bacteria linked with lung cancer risk in nonsmokers
Lower oral microbiome diversity and an abundance of specific taxa in the respiratory tract may be associated with greater risk for lung cancer in never smokers, researchers reported in Thorax.
“Bacterial communities have been detected in lung tissues and bronchoalveolar lavage samples and may be associated with the risk of nonmalignant and malignant respiratory diseases,” H. Dean Hosgood, PhD, associate professor in the department of epidemiology and population health at Albert Einstein College of Medicine, Bronx, New York, and colleagues wrote. “To assess the temporality between oral microbiome diversity and lung cancer risk, we evaluated bacterial diversity and abundance using metagenomic shotgun sequencing on noninvasive oral rinse samples that were collected among never smokers at baseline as part of two large prospective cohort studies.”
Researchers conducted a nested case-control study within the prospective cohort Shanghai Women’s Health Study (n = 74,941) and the Shanghai Men’s Health Study (n = 61,480), all of whom were lifetime never smokers without cancer at baseline and follow-up every 2 to 3 years after study entry in 1996 to 2006.
At enrollment, participants rinsed their mouths to provide a profile of the resident bacteria and information was collected on lifestyle, diet, medical history, and other environmental and workplace factors.
Ninety women and 24 men developed lung cancer within an average of 7 years. The researchers matched these cases with 114 nonsmokers without lung cancer of similar sex and age.
The researchers analyzed oral microbiome community structure and abundance and estimated the association of lung cancer risk, microbiome diversity and abundance of taxa.
Comparison of both sets of oral rinse samples showed that the microbiome differed between the two groups, according to a press release.
In those with lower microbiome diversity, the researchers reported an increased risk for lung cancer compared with those with high microbiome diversity.
A larger volume of particular types of species was also associated with lung cancer risk, according to the release. A greater abundance of Spirochaetia (OR high = 0.42; 95% CI, 0.21-0.85) and Bacteroidetes (OR high = 0.31; 95% CI, 0.15-0.64) was associated with a lower risk for lung cancer among never smokers after accounting for multiple comparisons. A greater abundance of the Bacilli class (OR high = 2.4; 95% CI, 1.18-4.87) and Lactobacillales order (OR high = 3.26; 95% CI, 1.58-6.7) was associated with an increased risk for lung cancer among never smokers, according to the results.
The associations remained when the analysis was restricted to participants who had not taken any antibiotics in the 7 days before samples were collected and also after excluding those diagnosed with lung cancer within 2 years of providing a sample, according to the release. The researchers noted that this was an observational study so it cannot establish cause. They also cautioned that, “[w]hile our study provides evidence that variation in the oral microbiome plays a role in lung cancer risk, the interpretation of our study must be done while considering the caveat that our findings are from a single point in a single geographical region.”
The researchers also noted in the release that this study raises several questions, such as the stability of the human oral microbiome over time, what determines the variability if the oral microbiome varies over time and how the ambient environment affects these microbiomes.
“Given the novelty of our findings and our limited sample size, replications studies are essential,” the researchers wrote. “Overall, our results highlight the need for further research on the role microbiota of the oropharyngeal and respiratory tract play in respiratory diseases.”