Background: With the development of technologies to look at the expression levels of hundreds of miRNAsat a time and the clear role of miRNAs in cancers, groups began looking at miRNAs profiles of different cancers,especially the circulating miRNAs. We intended to make sure whether circulating miRNAs could be a promisingbiomarker of human cancers. Method: We comprehensively searched the Cochrane Library, Medline and EMbasefrom 1966 to Nov 2009 for the following terms: (“miRNA” or “microRNA”) and (“tumor” or “carcinoma”) and(“plasma*” or “serum” or “circulating”). Detailed information was extracted from studies that met the inclusioncriteria: blood-based miRNAs in human cancers and studies published in the English literature. Results: Thecurrent review show that different researches use different measurement methods which might impact the results;Cancers treatment might have an affect on circulating miRNAs; some miRNAs are multi-faceted RNA; smallsample size might produce selection bias. Furthermore, because of the lack of randomized controlled trials andthe heterogeneous nature of the available data, no attempt was made to perform quantitativemeta-analyses. Conclusions: In this review, based on those researches, circulating miRNAs are promising and difficulties fortheir future application for diagnosing human cancers.
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