title: Effect of duration of fixation on quantitative reverse transcription polymerase chain reaction analyses.
abstract: Increasingly, there is the need to analyze gene expression in tumor tissues and correlate these findings with clinical outcome. Because there are few tissue banks containing enough frozen material suitable for large-scale genetic analyses, methods to isolate and quantify messenger RNA (mRNA) from formalin-fixed, paraffin-embedded tissue sections are needed. Recovery of RNA from routinely processed biopsies and quantification by the polymerase chain reaction (PCR) has been reported; however, the effects of formalin fixation have not been well studied. We used a proteinase K-salt precipitation RNA isolation protocol followed by TaqMan quantitative PCR to compare the effect of formalin fixation for 24, 48, and 72 hours and for 1 week in normal (2), oral epithelial dysplasia (3), and oral squamous cell carcinoma (4) specimens yielding 9 fresh and 36 formalin-fixed samples. We also compared mRNA and protein expression levels using immunohistochemistry for epidermal growth factor receptor (EGFR), matrix metalloproteinase (MMP)-1, p21, and vascular endothelial growth factor (VEGF) in 15 randomly selected and routinely processed oral carcinomas. We were able to extract RNA suitable for quantitative reverse transcription (RT) from all fresh (9/9) and formalin-fixed (36/36) specimens fixed for differing lengths of time and from all (15/15) randomly selected oral squamous cell carcinoma. We found that prolonged formalin fixation (>48 h) had a detrimental effect on quantitative RT polymerase chain reaction results that was most marked for MMP-1 and VEGF but less evident for p21 and EGFR. Comparisons of quantitative RT polymerase chain reaction and immunohistochemistry showed that for all markers, except p21, there was good correlation between mRNA and protein levels. p21 mRNA was overexpressed in only one case, but protein levels were elevated in all but one tumor, consistent with the established translational regulation of p21. These results show that RNA can be reliably isolated from formalin-fixed, paraffin-embedded tissue sections and can produce reliable quantitative RT-PCR data. However, results for some markers are adversely affected by prolonged formalin fixation times.
authors.affiliation: Oral Pathology, Department of Stomatology, University of California San Francisco, California 94143-0424, USA.
authors.forename: Maricris
authors.initials: M
authors.lastname: Macabeo-Ong
authors.forename: David G
authors.initials: DG
authors.lastname: Ginzinger
authors.forename: Nusi
authors.initials: N
authors.lastname: Dekker
authors.forename: Alex
authors.initials: A
authors.lastname: McMillan
authors.forename: Joseph A
authors.initials: JA
authors.lastname: Regezi
authors.forename: David T W
authors.initials: DT
authors.lastname: Wong
authors.forename: Richard C K
authors.initials: RC
authors.lastname: Jordan
mesh_terms: D002294:Carcinoma, Squamous Cell / Q000175:diagnosis / Q000235:genetics / Q000378:metabolism; D016228:Endothelial Growth Factors / Q000235:genetics / Q000378:metabolism; D005557:Formaldehyde; D015870:Gene Expression; D018773:Genes, erbB-1 / Q000502:physiology; D006801:Humans; D007150:Immunohistochemistry; D036341:Intercellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism; D008222:Lymphokines / Q000235:genetics / Q000378:metabolism; D020781:Matrix Metalloproteinase 1 / Q000235:genetics / Q000378:metabolism; D009062:Mouth Neoplasms / Q000175:diagnosis / Q000235:genetics / Q000378:metabolism; D016612:Paraffin Embedding; D012333:RNA, Messenger / Q000032:analysis*; D012334:RNA, Neoplasm / Q000032:analysis*; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D013997:Time Factors; D016707:Tissue Fixation / Q000379:methods*; D042461:Vascular Endothelial Growth Factor A; D042442:Vascular Endothelial Growth Factors; D020741:rho GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D016228:Endothelial Growth Factors; D036341:Intercellular Signaling Peptides and Proteins; D008222:Lymphokines; D012333:RNA, Messenger; D012334:RNA, Neoplasm; D042461:Vascular Endothelial Growth Factor A; D042442:Vascular Endothelial Growth Factors; D005557:Formaldehyde; D020781:Matrix Metalloproteinase 1; D020741:rho GTP-Binding Proteins