Oral microbes and gastrointestinal cancers: new strategies and insights

Gastrointestinal (GI) cancers are among the most prevalent cancers globally and represent a leading cause of cancer-related mortality. A distinctive characteristic of these cancers is their association with the microbes. Gut microbiota dysbiosis is widely recognized as a contributing factor in cancer development. Recent advancements in molecular techniques have increasingly underscored the role of oral microbes in GI cancers, especially colorectal cancer. Oral microbes, transported to the gut via swallowed saliva, have been shown to influence GI health. Both in vivo and in vitro investigations demonstrated the impacts of oral microbes in GI cancers. This review explores the changes in oral microbial diversity and relative abundance in esophageal, gastric and colorectal cancers as well as the underlying mechanisms. These mechanisms include immunomodulation, epigenetics, apoptosis, and others. Among these, immunomodulation stands out due to its close connection with cancer treatment. Finally, we discuss the limitations of the current research and propose new perspectives and directions for future studies.