Gastric cancer is among the leading causes of cancer related death worldwide. Patients with gastric cancer are typically asymptomatic, and diagnosed at late stages, supporting the need for the identification of novel prognostic and diagnostic biomarkers. Recently, microRNAs have emerged as molecular regulators that can play key roles in pathogenesis and progression of different malignancies, including gastric cancer. There is a growing body of evidence showing the aberrant activation of some known circulating miRNAs, e.g. let-7a, miR-21, miR-16, miR-93, miR- 103, miR-192a s well as tissue specific-miRNAs, e.g. miR-18a, miR-10b, miR-544, miR-195, miR-378, miR-34a, miR-145 in patients affected by gastric cancer, which involved with modulation of gastric-cancer-associated genes. In addition, there are mounting evidences on the value of miRNAs which are detected to be associated with drug-resistance mechanisms; suggesting their modulation as a potential approach to overcome chemo-resistance. Attuned with these facts, in this review we highlight several recent preclinical and clinical studies performed on circulating and tissue-specific miRNAs as promising biomarkers for detection of patients at early stages, prediction of prognosis, and monitoring of the patients in response to therapy.

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Background:Both microRNAs (miRNAs) and long noncoding RNAs (lncRNAs) have been shown to have a critical role in the regulation of cellular processes such as cell growth and apoptosis, as well as cancer progression and metastasis. lncRNAs are aberrantly expressed in many diseases including cancer. Although it is well known that miRNAs can target a large number of protein-coding genes, little is known whether miRNAs can also target lncRNAs. In the present study, we determine whether miR-21 can regulate lncRNA cancer susceptibility candidate 2 (CASC2) in colorectal cancer.Materials and Methods:LS174T cells were transfected with locked nucleic acid (LNA)-anti-miR-21 and scrambled LNA for 24, 48 and 72 h. The expression of miR-21 and lncCASC2 was evaluated by quantitative reverse transcriptase polymerase chain reaction.Results:However, contrary to what we expected and reported by others, lncCASC2 quantity was significantly reduced in LNA treated LS174T cells compared to the scrambled treated and normal untreated cells (P < 0.05).Conclusion:The interaction of miRNA and lncRNA are not as simple as suggested by other reports. Moreover, it could be complex molecular mechanisms underlying the communication of various noncoding RNA elements.