Microorganism Lung Cancer

Lung cancer is the most common cancer worldwide, and the leading cause of cancer-related morbidity and mortality1. Cigarette smoking is firmly established as a causative agent for lung cancer, although about 80 percent of people who develop lung cancer nowadays are non-smokers 2,3. Inflammatory lung processes, such as obstructive pulmonary disease, emphysema, chronic bronchitis, pneumonia and tuberculosis are also known risk factors for lung cancer, with significant effects observed for pneumonia and tuberculosis among never smokers4,5,6.
The role of microorganisms as single pathogens in carcinogenesis is known for a long time, with 15% of the global cancer burden attributable to infectious agents7. Gastric cancer has been the model of bacterially
Compelling evidence shows that an altered microbiome, termed dysbiosis, works as a driving force in inflammation and carcinogenesis13,14,15. Gastrointestinal tract microbiome represents 99% of the human microbial mass and is the best-investigated of all microbiomes16. Other organs with a well-characterized microbiome include the skin and the vagina17,18. Several mechanisms contribute to host-microbiota homeostasis and symbiotic relationships, and a dysregulation in this eubiotic environment leads to barrier failing, inflammation and dysbiosis19. A well-known example of this unbalance is the Clostridium difficile infection, which only causes disease when the native gut microbiota is suppressed by antibiotics20. Different compositions of mucosal adhering bacteria have been found in patients that harbor colonic adenomas or cancer, compared to healthy controls21. Interestingly, although most of the studies, in patients and animal models, show tumor-promoting effects of the bacterial microbiota, antitumor effects have also been observed22.
Culture-independent analysis using next-generation sequencing has been the lever to understanding bacterial microbiome and its key role in carcinogenesis17. Microbiome, i.e., the collective genome of all bacteria, archaea, fungi, protists, and viruses from a specific location, allowed the leap from detection and identification of individual microbes
It is known that chronically diseased airways are associated with an increased number of species, often with a shift away from the Bacteroidetes phylum, which dominates the healthy lung microbiome, towards Proteobacteria, the phylum that contains many familiar lung-associated gram-negative bacilli25. Although, there are few studies on microbiome and lung cancer12,26,27, evidence is starting to show differences in the bacterial communities of patients with malignant versus benign lesions, and the genera Veillonella and Megasphaera start to emerge as potential biomarkers on lung cancer27. So far, studies on neoplastic lung microbiome have been focused on sputum and bronchoalveolar lavage specimens, which may not reproduce the exact parenchymal microbiome.

In conclusion, there are considerable gaps in our knowledge about the role of microbiota in lung carcinogenesis. Going into a deep characterization of the lung microbiome will provide further data important to better understand its role in carcinogenesis and will subsequently contribute to new possibilities for diagnostic, preventive and therapeutic