Gene expression analysis using long-term preserved formalin-fixed and paraffin-embedded tissue of non-small cell lung cancer.

This study was performed to evaluate RNA extraction and gene expression analysis of non-small cell lung cancer (NSCLC) using formalin-fixed and paraffin-embedded (FFPE) specimens stored for more than 20 years by quantitative PCR (qPCR) and DNA microarrays. Long-term preserved FFPE materials enable large retrospective studies correlating molecular features with therapeutic response and clinical outcome. qPCR was used to evaluate RNA extraction methods and to compare DNA microarray gene expression profiles of FFPE and fresh frozen (FF) tissue. The Ambion RecoverAll kit appeared to be suited for RNA extraction of long-term preserved FFPE tissues. Microarray analysis using the Affymetrix platform displayed a high degree of correlation for endogenous control genes comparing FF and FFPE tissues and identified known NSCLC signature genes in both specimens. We conclude that high quality gene expression signatures can be recognized using the Affymetrix gene expression platform on FFPE tissue stored for more than 20 years. However, a general interpretation must be done with caution as different FFPE procedures have varying effects on RNA quality.