Investigating the role of intratumoral Streptococcus mitis in gastric cancer progression: insights into tumor microenvironment.

Growing evidence implicates that intratumoral microbiota are closely linked to cancer progression; however, research on the role of these microbiota in the development of gastric cancer remains limited. Here, using 16 S rRNA sequencing, tumor tissue proteomics and serum cytokines analysis, we identified enrichment of specific microbial communities within tumors of gastric cancer patients, possibly affecting the tumor microenvironment by immune modulation, metabolic processes, and inflammatory responses. Based on the results of in vivo experiments and intratumoral microbiota analysis, we found that Streptococcus mitis can inhibit gastric cancer progression via suppressing M2 macrophage polarization and infiltration, as well as altering the intratumoral microbial community. In summary, our findings suggest that the intratumoral microbiota, exemplified by Streptococcus mites, may be involved in regulating the progression of gastric cancer, thereby emerging as potential therapeutic targets for this disease.