Narrative review: respiratory tract microbiome and never smoking lung cancer.

Background and Objective: The lung microbiome was previously thought to be a sterile environment where only gaseous exchange takes place, but recent studies have shown the presence of microbiota in the lung. This review investigates the current literature on the effects of an environmental driven dysbiosis on the healthy oral and respiratory microbiome and its relationship to lung cancer risk in never-smokers. Methods: An online electronic search was performed on PubMed of all English-language literature using combinations of the following keywords: "lung cancer", "dysbiosis", "non-smokers", "oral microbiome", and "respiratory microbiome". All population-based studies reporting results on oral and/or respiratory microbiome in adults were considered for our narrative review. Key Content and Findings: Metagenomic analyses have been performed on isolated samples from healthy participants and compared to samples from those with lung cancer. Research shows that a decrease in alpha diversity of microbes in the oral microbiome is associated with increased risk of lung cancer, along with differences in beta diversity in the sputum of lung cancer cases and healthy controls. Further, several studies have observed that significant changes in the abundance of genera such as increased abundance of Conclusions: These findings suggest potential carcinogenic processes such as increased inflammation associated with changes in flora. Additionally, studies showed that increase in certain taxa such as