Role of the microbiome in the development and treatment of gastric cancer: an overview of the biological and clinical landscape

For decades, the stomach was considered a sterile organ, due to the acid environment. However, starting from the discovery of Helicobacter pylori, this concept has progressively refined. By damaging the hydrochloric acid-secreting glands, H. pylori infection primes the progression from acute to chronic inflammation in gastric mucosa resulting in atrophic gastritis, intestinal metaplasia, dysplasia and ultimately gastric cancer (GC). Due to the challenging identification of culturing bacteria, the carcinogenic role of gastric microbial community, other than H. pylori, remains underestimated. More recently, a growing body of evidence has pointed out the dynamism of gastric microbiota as a crucial step for GC development, besides elucidating some additional activity in modulating the efficacy of cancer treatments. In turn, anticancer therapies can shape gastric microbiota with consequent dysbiosis and a potential correlation with drug-related toxicity. In conclusion, the current review aims to deepen the role of gut microbiota as a key factor in gastric disease at multiple levels, from carcinogenesis to the metastatic phase. It also provides novel insights on gastric microbiota as potential target for tailoring multimodal strategies, either surgical or oncological, to finally provide our patients with more individualized treatment options.