Objective To detect the expression of copine 1 (CPNE1) in the gastric cancer (GC) and investigate its association with prognosis. MethodsThe clinicopathologic data of 121 patients who underwent radical gastrectomy in the Department of General Surgery, The 940th Hospital of Joint Logistics Support Force of Chinese People’s Liberation Army from March 2017 to December 2018 were retrospectively collected. The protein expression of CPNE1 in the GC tissues was detected by immunohistochemical (IHC) staining, and its association with prognosis was analyzed. GC tissues and adjacent tissues samples from 16 patients in the same time were prospectively collected, and the mRNA and protein expressions of CPNE1 were detected by real-time quantitative reverse transcription polymerase chain reaction (RT-qPCR) and Western blot (WB), respectively. Multivariate Cox proportional hazards regression model was used to analyze the prognostic factors of GC patients. ResultsIHC staining results showed that the CPNE1 was mainly expressed in the cell membrane and cytoplasm of gastric epithelial cells, and the color showed different degrees of brown. Among the 121 patients, 70 (57.9%) had high CPNE1 protein expression and 51 (42.1%) had low CPNE1 protein expression. The RT-qPCR and WB results of 16 pairs of fresh tissue specimens showed that the expression levels of CPNE1 mRNA and protein in the GC tissues were higher than those in the corresponding adjacent tissues (CPNE1 mRNA mean value: 1.451 vs. 1.100, P=0.048; CPNE1 protein mean value: 0.995 vs. 0.521, P=0.001). The multivariate Cox proportional hazards regression analysis showed that the high protein expression of CPNE1 [HR (95%CI)=1.931 (1.123, 3.321), P=0.017] was the risk factor affecting the prognosis of the patients with GC. ConclusionCPNE1 highly expresses in GC tissues and is associated with a poor prognosis in patients with GC, and it may be a potential tumor biomarker.