Abstract
Recent research on cancer-associated microbial communities has elucidated the interplay between bacteria, immune cells, and tumor cells; the bacterial pathways involved in the induction of carcinogenesis; and their clinical significance. Although accumulating evidence shows that a dysbiotic condition is associated with lung carcinogenesis, the underlying mechanisms remain unclear. Microorganisms possibly trigger tumor initiation and progression, presumably via the production of bacterial toxins and other pro-inflammatory factors. The purpose of this review is to discuss the basic role of the airway microbiome in carcinogenesis and the underlying molecular mechanisms, with the aim of developing anticancer strategies involving the airway microbiota. In addition, the mechanisms via which the microbiome acts as a modulator of immunotherapies in lung cancer are summarized.
Highlights
The human microbiome consists of more than 1000 species of bacteria inhabiting the human body, including the skin, oral cavity, nasal cavity, stomach, small intestine, large intestine, urinary tract, and vagina [1]
The human host and the intestinal microbiome are in a symbiotic relationship, which is mutually beneficial for maintaining homeostasis [2]
These findings suggest the involvement of host-specific lung microbiomes in the pathogenesis of respiratory diseases such as Chronic Obstructive Pulmonary Disease (COPD) and lung cancer via induction of local inflammatory changes
Summary
The human microbiome consists of more than 1000 species of bacteria inhabiting the human body, including the skin, oral cavity, nasal cavity, stomach, small intestine, large intestine, urinary tract, and vagina (hundreds of trillions of bacteria in number) [1]. The operational taxonomic unit (OTU) is a measure of sequence similarity, and an OTU similarity of ≥97% is considered to indicate evolutionarily identical bacterial species [28] This key development allows the characterization of species in lower airway samples without the prior prediction of the species that might be present. Lower airway samples from patients with COPD and bronchial asthma and healthy individuals were subjected to 16S rRNA gene sequencing, and the microbiome profiles of patients with respiratory disease and healthy individuals were compared [22]. An analysis of samples collected from different parts of the lungs of patients with severe COPD excised during transplantation showed obvious microbiome heterogeneity among lung lobes [34] These findings suggest the involvement of host-specific lung microbiomes in the pathogenesis of respiratory diseases such as COPD and lung cancer via induction of local inflammatory changes
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