DNA Extraction from Formalin-Fixed, Paraffin-Embedded Tissue

Introduction

Formalin-fixed, paraffin-embedded (FFPE) tissue is one of the most widely practiced methods for clinical sample preservation and archiving. It is estimated that, worldwide, over a billion tissue samples, most of them FFPE, are being stored in numerous hospitals, tissue banks, and research laboratories. These archived samples could potentially provide a wealth of information in retrospective molecular studies of diseased tissues. While standard for histopathology and microscopic investigation (e.g., hematoxylin and eosin [H&E] staining, immunohistochemistry [IHC], and tissue microarray [TMA]), FFPE samples pose a major challenge for molecular pathologists, because nucleic acids are heavily modified and trapped by extensive protein-nucleic acid and protein-protein cross linking. Historically, FFPE samples were not considered to be a viable source for molecular analyses. Recently, however, it has been discovered that with appropriate protease digestion, it is possible to release microgram amounts of DNA and RNA from FFPE samples. The purified nucleic acids, although highly fragmented, are suitable for a variety of downstream genomic and gene expression analyses, such as polymerase chain reaction (PCR), quantitative reverse transcription PCR (qRT-PCR), microarray, array comparative genomic hybridization (CGH), microRNA, and methylation profiling. Several commercial kits are currently available for FFPE extraction. The protocol reported here is adapted from the Ambion RecoverAll Total Nucleic Acid Isolation Kit, but includes several modifications. Although our protocol focuses on DNA isolation, the RecoverAll Kit can also be utilized to recover RNA, including microRNA.