Evaluation and validation of total RNA extraction methods for microRNA expression analyses in formalin-fixed, paraffin-embedded tissues.

Histopathology archives of well-annotated formalin-fixed, paraffin-embedded (FFPE) tissue specimens are valuable resources for retrospective studies of human diseases. Since recovery of quality intact mRNA compatible with molecular techniques is often difficult due to degradation, we evaluated microRNA (miRNA), a novel class of small RNA molecules with growing therapeutic and diagnostic potential, as an alternative analyte for gene expression studies of FFPE samples. Analyzing total RNA yield, miRNA recovery, and robustness of real-time polymerase chain reaction for miRNA, mRNA, and rRNA species, we compared the performance of commercially available RNA isolation kits and identified a preferred methodology.