Most tumors of the digestive system, including esophageal, gastric, liver and colorectal cancer, are malignant tumors that are associated with rates of high morbidity and mortality. The lack of effective methods for early diagnosis is an important cause of poor prognosis for these malignancies. Circular RNAs (circRNAs) belong to a family of endogenous, covalently closed non-coding RNAs that are characterized as having no 5 ' cap structures or 3 ' poly-A tails. Shortly following discovery, circRNAs were considered to be a product of mis-splicing and have no significant biological function. However, in recent years, accumulating evidence is demonstrating that they serve key roles in tumorigenesis and have the potential to serve as diagnostic markers. The present article summarizes the biogenesis and function of circRNAs and reviews their role in seven common types of tumor of the digestive system whilst exploring their potential as tumor markers and the significant roles they can serve in the digestive system, in addition to providing a referencing point for future studies of digestive system malignancies.

Gastric cancer (GC) is one of the most common cancer types and the fourth leading cause of cancer-related mortality among all malignant tumors worldwide. Due to insidious onset and lack of reliable early diagnostic markers, most GC patients are at an advanced stage at the time of diagnosis. Annexin is an evolutionally-conserved Ca2+-dependent phospholipid-binding protein superfamily, including five members (A, B, C, D, and E). Annexins in the cells of vertebrates comprised the annexin A family, consisting of 12 members in humans. The biological functions of annexin A are Ca2+-signal transduction, vesicle transport, cell proliferation, cell division, cell apoptosis, signal transduction, anti-inflammatory, proangiogenesis, and anticoagulation, most of which overlap with the basic characteristics of tumors. Accumulating evidence indicated that members of the annexin A family are correlated with tumorigenesis and chemoresistance and can be used as potential tumor prognostic factors and targets for biological therapy. Thus, the current review focused on the role and relative mechanisms of the annexin A family in GC.

Background: Exosomes play an important role in transferring information among different cell types, as they transport materials from the cell membrane to the cytoplasm. They are involved not only in normal physiological functions, but also in the occurrence and development of a variety of diseases. Cancer is a major health problem affecting humans. Currently, exosomes are considered novel stars in tumor therapy.Objective: To present a review focusing on the role of exosomes in tumorigenesis and development and the possibility of treating tumors with exosome-targeted therapies or using exosomes as carriers.Methods: We reviewed literature related to the biological origin and function of exosomes and exosome-tumor relationship.Results: Exosomes are closely related to tumor immunity, angiogenesis, pre-metastasis microenvironment, chemoresistance, energy metabolism, etc. Tumor therapy involving the targeting of exosomes involves block the generation, secretion, uptake of exosomes, and elimination of circulating exosomes, and develop antitumor vaccines. Exosome as delivery vehicles can be loaded with chemotherapeutic drugs, therapeutic genes, and other therapeutic drugs to target cells. Prospects and challenges of exosome-based tumor therapy are also discussed.Conclusion: Exosomes are involved in multiple processes during tumor development and should be further studied as novel targets for cancer therapy.

The lack of new drugs and resistance to existing drugs are serious problems in gastric cancer(GC) treatment. The research found polyphenols possess anti-Helicobacter pylori(Hp) and antitumor activities and may be used in the research and development of drugs for cancer prevention and treatment. However, polyphenols are affected by their chemical structures and physical properties, which leads to relatively low bioavailability and bioactivity in vivo. The intestinal flora can improve the absorption, utilization, and biological activity of polyphenols, whereas polyphenol compounds can increase the richness of the intestinal flora, reduce the activity of carcinogenic bacteria, stabilize the proportion of core flora, and maintain homeostasis of the intestinal microenvironment. Our review summarizes the gastrointestinal flora-mediated mechanisms of polyphenol against GC.