MicroRNAs in Cancer

A frequent problem in the diagnosis of human tumors is the lack of biomarkers associated with biological processes that drive the initiation and progression of cancer. Evidences indicate that microRNAs (miRNAs) regulate the expression of different genes (post-transcriptional regulation) associated with carcinogenesis process. Because of this, small RNAs have become a crucial point in the molecular dissection of human cancer a few years ago. MiRNAs are small non-coding RNAs (19–24 nucleotides) responsible for fine-tuning of gene expression influencing the stability and efficiency of translation of messenger RNAs (mRNA) targets. Recently it has been proposed that the pathogenesis of cancer involves, among other macromolecules, miRNAs whose expression profiles are associated with prognosis and therapeutic results in various human cancers. The mechanisms mediating tumor progression exerted by miRNAs have been addressed only recently. MiRNAs exhibits a dual role in all types of cancer depending on their expression status i.e. up or down regulated. Thus, miRNAs may act as oncogenes (oncomirs) or tumor-suppressors. However, if the interest is to use miRNAs as biomarkers they should be ideally easily assayed with minimally invasive medical procedures but at the same time offering high sensitivity and specificity. In this context, recent findings suggest the potential of circulating miRNAs in the screening or monitoring cancer treatment.