Introduction: MicroRNAs (miRNAs) are new group of regulatory RNAs with approximately 22 nucleotides in length. The miRNAs have important role in human cancers and apparently function as either oncogenes or tumor suppressors. In this study, serum level of miR-21 was determined in patients with gastric adenocarcinoma and its correlation with tumor staging was assessed in the patients, for the first time, in Iran.

Materials & methods: The study was conducted on 40 patients with gastric adenocarcinoma and 40 control subjects who had referred to cancer institute due to gastrointestinal irritation but were diagnosed as healthy on noncancerous. Serum levels of miR‑21 were measured using a quantitative Real-time polymerase chain reaction (qRT-PCR) assay. The correlation of miR‑21  serum level with tumor staging was assessed in the patients.

Results: Serum level of miR‑21 was approximately 3.5 fold higher in patients with gastric adenocarcinoma than control subjects (P<0.0001). Increased level of miR-21 in serum was associated with clinical stages of tumors in the patients (&tau = 0.56, P < 0.01).

Discussion & Conclusions: Given the importance of miR‑21 in the progression of gastric adenocarcinoma and its correlation with clinicopathological factors, the serum level of miR-21 can be served as a new noninvasive diagnostic  biomarker for gastric adenocarcinoma.