MicroRNAs (miRNAs) represent a class of small non-coding RNAs that control gene 
expression by targeting messenger RNA (mRNA). Recently, it has been demonstrated 
that miRNA expression is altered in many human diseases including cancers, 
suggesting that miRNA may play a potential role in the pathogenesis of different 
diseases. It has also been reported that there is a unique expression pattern of 
miRNAs in the disease state differing from the normal state. In this review, we 
focus on the miRNA signatures in different human diseases including cancers. 
Such signatures may be used as diagnostic and prognostic markers.