Background: It was recently revealed that microRNAs (miRNAs) can stably exist in serum and may affect the pathogenesis of several diseases. However, there are few reports that have demonstrated the significance of miRNAs in the serum of patients with esophageal squamous cell carcinoma (ESCC). Thus, the aims of this study were to clarify the status of miRNA-21 in serum of ESCC patients and to reveal the usefulness of this molecule as a biomarker. Methods: We measured the miRNA-21 levels in serum samples from 71 ESCC patients and 39 healthy controls by using real-time RT-PCR. We also evaluated the changes in the miRNA-21 level during operation and chemotherapy. Results: We found that serum concentration of miRNA-21 in ESCC patients was significantly higher than that in healthy controls (P < 0.001). A significant reduction in the serum miR-21 levels was observed in the postoperative samples versus the preoperative samples (P = 0.003). Furthermore, miRNA-21 levels were significantly reduced in ESCC patients who responded to chemotherapy (P = 0.003), whereas no significant change was observed in the non-responders. Conclusion: Serum miRNA-21 is considered to be a novel biomarker for diagnosing ESCC, and it can also be used as a response marker during chemotherapy for ESCC patients.
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