Excavation of a buried treasure--DNA, mRNA, miRNA and protein analysis in formalin fixed, paraffin embedded tissues.

Fresh or frozen tissue samples will always be the best tissue source for the analysis of nucleic acids and proteins from tissues. However, their long-term storage is expensive and laborious. Much interest has therefore been focused on the question whether the almost infinite resources of formalin fixed and paraffin embedded tissue samples in the archives of pathology and histology departments can be used for research on biomarkers and molecular mechanisms of disease. In recent years the methods and protocols for the extraction of DNA, mRNA, miRNA and proteins from formalin-fixed and paraffin-embedded tissue samples have improved enormously. Especially, the possibilities of analysing DNA and miRNA in FFPE have reached a level that allows their application as a first line approach in the search for biomarkers. In contrast, many questions remain in terms of quantification of mRNA and protein expression levels in formalin-fixed and paraffin-embedded tissue samples. This review gives an overview on current potentials and limitations of the quantification of DNA, miRNA, mRNA and the proteome in FFPE tissue samples. The chemical events during formalin fixation and paraffin embedding and alternatives to formalin fixation are described. In addition, methods and general problems of DNA, miRNA, mRNA and protein extraction and the current knowledge on the feasibility and accuracy of quantitative gene expression analysis in FFPE tissues is summarized.