Pulmonary dysbiosis and lung cancer
Based on known correlations between intestinal dysbiosis and colorectal cancer on the one hand, and pulmonary dysbiosis and asthma or COPD on the other hand, a Chinese-American team focused on a new research approach: the link between pulmonary microbiota and lung cancer.
The lung is not the sterile organ we believed it to be only a few decades ago: its microbiota–now well documented–provides protection against infections and allergies. Nowadays, the field of studies on the links between infection, inflammatory state and carcinogenesis is rapidly growing.
An innovative comparison
To this end, researchers extracted bronchoscopic protected specimen brush samples from 24 patients with lung cancer, specifically unilateral samples of a pulmonary mass. One sample was taken from the cancerous site and another from a non-cancerous site. Samples were also taken, through bronchoscopy, from 18 healthy volunteers, included in the control group. The bacterial composition of each site was then determined through 16S rRNA sequencing. This was used to define the exact composition of the microbiota of the “cancerous” lung, the non-cancerous area of the lung and finally the “healthy” control lung.
Streptococcus vs. Staphylococcus
A significant decrease in microbiota diversity was observed in patients with cancer. In other words, there was an overabundance of the genus Streptococcus while the genus Staphylococcus was more abundant in the control group. As an additional result, the microbiota composition from the affected lung was not limited to the tumor site and was the same in non-cancerous areas from the same patient. Finally, a bacterial gradient was detected between both groups, suggesting a change in the microenvironment associated to the development of lung cancer. According to the researchers, it could be deduced, by extrapolation, that Streptococcus has a harmful role while Staphylococcus has a protective role in the development of cancer, although other studies led to contradictory results regarding the influence of these bacteria and their specific roles in the organ colonized in case of cancer. In any case, they concluded that prevention, diagnosis and therapeutic strategies implemented to face lung cancer should likely take into account the microbiota.
Liu, H.-X. et al. Difference of lower airway microbiome in bilateral protected specimen brush between lung cancer patients with unilateral lobar masses and control subjects. Int. J. Cancer 142, 769–778 (2018).