Comparative Changes in Fecal Microbiome After Endoscopic Resection and Surgical Resection in Gastric Cancer Patients

<b>Background/Objectives</b>: Gastric cancer treatments can lead to significant alterations to patients' gastrointestinal microbiome. However, differences in microbial impacts between gastrectomy and endoscopic submucosal dissection (ESD) remain underexplored. This study investigates how these treatments influence microbial diversity and composition in patients with stage I gastric cancer. <b>Methods</b>: Patients with pathologically confirmed stage I gastric cancer were recruited from Chung-Ang University Hospital between December 2016 and December 2019. This study analyzed fecal samples from 13 patients (ESD: <i>n</i> = 5; gastrectomy: <i>n</i> = 8) before and after treatment using 16S rRNA gene sequencing. Microbial diversity indices and taxonomic composition were compared, with follow-up extending up to two years. <b>Results</b>: In the total cohort, alpha diversity significantly decreased post-treatment (<i>p</i> < 0.05), and beta diversity analysis showed distinct clustering between pre- and post-treatment samples (<i>p</i> < 0.05). At the genus level, Bacteroides significantly decreased (<i>p</i> < 0.05), while Lactobacillus, Bifidobacterium, and Blautia showed significant increases (<i>p</i> < 0.05). Comparative analyses revealed that in the ESD group, alpha diversity remained unchanged, although beta diversity showed significant clustering (<i>p</i> < 0.05), without notable changes in major taxa. In contrast, surgical resection resulted in a significant reduction in alpha diversity (<i>p</i> < 0.05) and beta diversity clustering (<i>p</i> < 0.05), with increased abundances of Streptococcus and Blautia and decreased abundance of Bacteroides (<i>p</i> < 0.05). <b>Conclusions</b>: Surgical gastrectomy exerts significant effects on microbiome diversity and composition, while ESD has a more limited impact. These findings underscore the importance of considering microbiome changes in postoperative management.