AIM To determine whether circular RNAs(circ RNAs) are involved in pathological processes of gastric cancer(GC).METHODS Three circ RNAs with differential expression in GC and colorectal cancer were randomly selected for validation by quantitative reverse transcription-polymerase chain reaction(q RT-PCR), using 20 pairs of gastric tissues and normal tissues. Based on the predicted circ RNAmi RNA network, we then focused on hsa_circ_0000745, which was found to be down-regulated in 20 GC tissues compared with normal tissues. The hsa_circ_0000745 levels were further analyzed by q RT-PCR in 60 GC tissues and paired adjacent non-tumor tissues, as well as 60 plasma samples from GC patients and 60 plasma samples from healthy controls. The associations between the levels of hsa_circ_0000745 and the clinicopathological features of GC patients were statistically assessed. A receiver operating characteristic(ROC) curve was used to evaluate the diagnostic value of hsa_circ_0000745 in GC.RESULTS Hsa_circ_0000745 was down-regulated in GC tissues vs non-tumorous tissues(P < 0.001) and in plasma samples from patients with GC vs healthy controls(P < 0.001). The expression level of hsa_circ_0000745 in GC tissues correlated with tumor differentiation, while the expression level in plasma correlated with tumor-nodemetastasis stage. The area under the ROC curve(AUC) of hsa_circ_0000745 in plasma was 0.683, suggesting good diagnostic value. Plasma hsa_circ_0000745 level combined with carcinoembryogenic antigen(CEA) level increased the AUC to 0.775.CONCLUSION Hsa_circ_0000745 plays an important role in GC and its expression level in plasma in combination with CEA level is a promising diagnostic marker for this malignancy. AIM To determine whether circular RNAs (circ RNAs) are involved in pathological processes of gastric cancer (GC). METHODS Three circ RNAs with differential expression in GC and colorectal cancer were randomly selected for validation by quantitative reverse transcription-polymerase chain reaction Based on the predicted circ RNA RNA RNA network, we then focused on hsa_circ_0000745, which was found to be down-regulated in 20 GC tissues compared with normal tissues. The hsa_circ_0000745 levels were further analyzed by q RT-PCR in 60 GC tissues and paired adjacent non-tumor tissues, as well as 60 plasma samples from GC patients and 60 plasma samples from healthy controls. The associations between the levels of hsa_circ_0000745 and the clinicopathological features of GC patients were statistically assessed. A receiver operating characteristic (ROC) curve was used to evaluate the diagnostic value of hsa_circ_0000745 in GC.RESULTS Hsa_ circ_0000745 was down-regulated in GC tissues vs non-tumorous tissues (P <0.001) and in plasma samples from patients with GC vs. healthy controls (P <0.001). The expression level of hsa_circ_0000745 in GC tissues correlated with tumor differentiation, while the Expression level in plasma correlated with tumor-node metastasis stage. The area under the ROC curve (AUC) of hsa_circ_0000745 in plasma was 0.683, suggesting good diagnostic value. Plasma hsa_circ_0000745 level combined with carcinoembryogenic antigen (CEA) level increased the AUC to 0.775.CONCLUSION Hsa_circ_0000745 plays an important role in GC and its expression level in plasma in combination with CEA level is a promising diagnostic marker for this malignancy.