To explore the prognostic significance of CPNE3, we used the UALCAN and Kaplan–Meier plotter databases to analyze CPNE3 mRNA expression, which indicated that CPNE3 mRNA expression was considerably higher in GC tissues and was associated with poor OS, PPS, FP, and clinical stage in patients with GC (Supplementary Fig. S4A–E). This evidence concerns the gene CPNE3 and gastric cancer.