MicroRNA isolation from formalin-fixed, paraffin-embedded tissues.

MicroRNAs (miRNAs) are small (19-23nt), highly conserved noncoding RNAs that posttranscriptionally regulate target gene expression. Altered expression of miRNAs has been demonstrated in many different human diseases, including cancer. The large archives of formalin-fixed, paraffin-embedded (FFPE) tissue specimens with clinical follow-up information that exist are a highly valuable source of tissue to study human diseases. However, RNA in the FFPE tissue is fragmented and may be chemically modified. In this study, we prepared miRNA preserving total RNA from matched pairs of FFPE and respective fresh-frozen clinical samples, and used that in microarray experiments to compare miRNA expression profiles between FFPE and fresh-frozen tissue from the same tissue samples. We demonstrate that miRNA expression profile from FFPE tissues closely resembles that from fresh tissues. These results underscore the suitability of FFPE tissues as appropriate resources for miRNA expression analyses.