MicroRNAs (miRNAs or mirs) are small, non-coding RNAs that bind specific mRNAs and decrease their translation or increase their degradation. miRNAs may modulate the formation and maintenance of tumors by regulating oncogene and tumor suppressor expression. For example, overexpression of a subset of miRNAs has been inversely correlated with certain tumor phenotypes, suggesting a role in tumor suppression. Pairs of oncogenes and the corresponding miRNAs that attenuate their expression have been recently identified. These miRNAs, or "anti-oncomirs," can act as natural inhibitors of oncogene function, indicating the possibility that they might be developed as novel therapeutics.