The Gut Microbiome As a Biomarker of Cancer Progression among Female Never-smokers with Lung Adenocarcinoma

Background: The gut microbiome plays an important role in the immune system and has attracted attention as a biomarker of various diseases, including cancer. As such, we examined the relationship between the gut microbiome and lung cancer progression. In addition, we assessed the correlation between the gut microbiome and epidermal growth factor receptor (EGFR) mutation status.Methods: Female never-smokers diagnosed with lung adenocarcinoma were consecutively and prospectively enrolled between May 2018 and August 2019. Fecal samples were collected within 1 month before or after diagnosis and before administration of any lung cancer treatment. Principal coordinate analyses were retrospectively performed using Bray-Curtis distance matrices to investigate the effects of clinical variables (age, body mass index, Tumor-Node-Metastasis stage, T category, N category, M category, primary tumor size, performance status, and EGFR mutation status) on the gut microbial community. A correlation analysis was also performed to determine the strength of association between the dominant taxonomy (comprising ≥1% of the relative abundance of bacterial DNA sequences) and clinical variables.Results: A total of 37 patients were enrolled. T category and primary tumor size were significantly correlated with the gut microbial community (p=0.018 and 0.041, respectively). At the genus level, a significant positive correlation was observed between the relative abundance of Faecalibacterium and both T category (correlation coefficient, R=0.51, p=0.0013) and primary tumor size (R=0.37, p=0.024), whereas a significant negative correlation was observed between the relative abundances of Fusicatenibacter and Bacteroides and T category (R=−0.35, p=0.034 and R=−0.32, p=0.05, respectively) and primary tumor size (R=−0.36, p=0.029 and R=−0.41, p=0.012, respectively). EGFR mutation status had no statistically significant effect on the gut microbial community (p=0.11). However, the relative abundances of Bifidobacterium and Faecalibacterium were significantly higher in EGFR mutation–negative patients than EGFR mutation–positive patients (p=0.012 and 0.041), whereas the relative abundance of Blautia was significantly lower in EGFR mutation–negative patients (p=0.036).Conclusions: This is the first study identifying the gut microbiome as a promising biomarker of lung cancer progression. Further elucidation of the role of the gut microbiome in lung cancer progression could facilitate development of new treatments for lung cancer.