Background: Altered expression of miR-503 has been linked to human carcinogenesis. In this present study, we aimed to detect the potential for miR-503 as a novel biomarker for gastric cancer (GC) patients.
Materials and methods: The relative mRNA level of miR-503 in serum and tissue of 68 GC patients and serum of 32 healthy volunteers was determined by real-time reverse transcription quantitative polymerase chain reaction. 
Results: The miR-503 level was significantly lower in the tissue and serum of GC than their counterparts (all P <0.01). Downregulation of miR-503 was found to be corrected with more aggressive tumor. Patients in the high-miR-503 group showed significantly better overall survival compared to the low-miR-503 group (P =0.021). The serum miR-503 level in GC was inversely correlated with carcinoembryonic antigen (CEA) (r =−0.624, P <0.001). Furthermore, the area under the receiver operating characteristic curve for miR-503 discriminating GC patients from healthy individuals was 0.889 (P =0.006), with a sensitivity of 96.8% and a specificity of 79.4%, higher than that of CEA (area under the receiver operating characteristic curve =0.681, P =0.048).
Conclusion: The present study suggests that the expression level of miR-503 may serve as prognostic and diagnostic biomarker for GC.
Keywords: microRNA, gastric cancer, diagnosis, prognosis, biomarker