Formalin-fixed And Paraffin-embedded Materials Research Articles

Impact of antigen retrieval protocols on the immunohistochemical detection of epigenetic DNA modifications

This study compares three different pretreatment protocols for the immunohistochemical detection of 5-methylcytosine (5-mC) and 5-hydroxymethylcytosine (5-hmC) in nuclear DNA. The human biological samples analyzed included formalin-fixed and paraffin-embedded (FFPE) normal squamous epithelium, ethanol-fixed cultured cells, and metaphase chromosomes. The antigen retrieval methods included low pH Citrate and high pH Tris–ethylenediaminetetraacetic acid (EDTA) protocols, as well as a method using Pepsin pretreatment combined with HCl for DNA denaturation. A gradual increase in the detection levels of 5-mC and 5-hmC was observed when going from Citrate via Tris/EDTA to Pepsin/HCl retrieval. While the Citrate retrieval protocol was the least efficient for the detection of 5-mC and 5-hmC, it did preserve nuclear morphology and enabled visualization of differences in intra- and internuclear distribution patterns in tissue and cell culture samples by single- and double-fluorescence detection. Quantification of (hydroxy)methylation levels in FFPE material demonstrated a significant heterogeneity and differences in 5-mC and 5-hmC levels within and between nuclei in the different compartments of normal squamous epithelium. It was concluded that immunohistochemical detection of 5-mC and 5-hmC enables the correlation of these DNA modifications with histomorphological features in heterogeneous tissues, but this is influenced by different pretreatment protocols that must be carefully chosen to allow an appropriate interpretation of these epigenetic switches.

The mutational signatures of formalin fixation on the human genome

Clinical archives of patient material near-exclusively consist of formalin-fixed and paraffin-embedded (FFPE) blocks. The ability to precisely characterise mutational signatures from FFPE-derived DNA has tremendous translational potential. However, sequencing of DNA derived from FFPE material is known to be riddled with artefacts. Here we derive genome-wide mutational signatures caused by formalin fixation. We show that the FFPE-signature is highly similar to signature 30 (the signature of Base Excision Repair deficiency due to NTHL1 mutations), and chemical repair of DNA lesions leads to a signature highly similar to signature 1 (clock-like signature due to spontaneous deamination of methylcytosine). We demonstrate that using uncorrected mutational catalogues of FFPE samples leads to major mis-assignment of signature activities. To correct for this, we introduce FFPEsig, a computational algorithm to rectify the formalin-induced artefacts in the mutational catalogue. We demonstrate that FFPEsig enables accurate mutational signature analysis both in simulated and whole-genome sequenced FFPE cancer samples. FFPEsig thus provides an opportunity to unlock additional clinical potential of archival patient tissues.

MALDI Mass Spectrometry Imaging for the Distinction of Adenocarcinomas of the Pancreas and Biliary Tree.

Pancreatic ductal adenocarcinoma and cholangiocarcinoma constitute two aggressive tumor types that originate from the epithelial lining of the excretory ducts of the pancreatobiliary tract. Given their close histomorphological resemblance, a correct diagnosis can be challenging and almost impossible without clinical information. In this study, we investigated whether mass spectrometric peptide features could be employed to distinguish pancreatic ductal adenocarcinoma from cholangiocarcinoma. Three tissue microarrays of formalin-fixed and paraffin-embedded material (FFPE) comprising 41 cases of pancreatic ductal adenocarcinoma and 41 cases of cholangiocarcinoma were analyzed by matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI). The derived peptide features and respective intensities were used to build different supervised classification algorithms: gradient boosting (GB), support vector machine (SVM), and k-nearest neighbors (KNN). On a pixel-by-pixel level, a classification accuracy of up to 95% could be achieved. The tentative identification of discriminative tryptic peptide signatures revealed proteins that are involved in the epigenetic regulation of the genome and tumor microenvironment. Despite their histomorphological similarities, mass spectrometry imaging represents an efficient and reliable approach for the distinction of PDAC from CC, offering a promising complementary or alternative approach to the existing tools used in diagnostics such as immunohistochemistry.

Reproducible Lipid Alterations in Patient-Derived Breast Cancer Xenograft FFPE Tissue Identified with MALDI MSI for Pre-Clinical and Clinical Application.

The association between lipid metabolism and long-term outcomes is relevant for tumor diagnosis and therapy. Archival material such as formalin-fixed and paraffin embedded (FFPE) tissues is a highly valuable resource for this aim as it is linked to long-term clinical follow-up. Therefore, there is a need to develop robust methodologies able to detect lipids in FFPE material and correlate them with clinical outcomes. In this work, lipidic alterations were investigated in patient-derived xenograft of breast cancer by using a matrix-assisted laser desorption ionization mass spectrometry (MALDI MSI) based workflow that included antigen retrieval as a sample preparation step. We evaluated technical reproducibility, spatial metabolic differentiation within tissue compartments, and treatment response induced by a glutaminase inhibitor (CB-839). This protocol shows a good inter-day robustness (CV = 26 ± 12%). Several lipids could reliably distinguish necrotic and tumor regions across the technical replicates. Moreover, this protocol identified distinct alterations in the tissue lipidome of xenograft treated with glutaminase inhibitors. In conclusion, lipidic alterations in FFPE tissue of breast cancer xenograft observed in this study are a step-forward to a robust and reproducible MALDI-MSI based workflow for pre-clinical and clinical applications.

Highly Sensitive Droplet Digital PCR Method for Detection of de novo EGFR T790M Mutation in Patients with Non-Small Cell Lung Cancer.

ObjectiveThe aim of this study was to investigate the allelic relation between de novo T790M and concomitant sensitizing EGFR mutations in EGFR-TKIs naïve NSCLCs and to explore whether the formalin-fixed and paraffin-embedded (FFPE) materials affect the detection of de novo EGFR T790M mutation.MethodsSpecimens of 300 consecutive EGFR-TKI naïve NSCLCs who received surgical resection between January 2016 and June 2018 were retrospectively investigated. All the snap-frozen tumor tissues from 300 NSCLCs were screened by droplet digital PCR (ddPCR) for the detection of de novo T790M mutation. The allelic relation between de novo T790M mutation and concomitant sensitizing EGFR mutations was also investigated. Furthermore, we assessed de novo T790M mutation in paired FFPE specimens of 50 patients which included tumor tissues and paired normal lung tissues of the pretreatment NSCLCs to investigate whether FFPE materials affect the detection of de novo T790M mutation.ResultsThe de novo T790M mutation was observed in four patients which included one patient of single de novo T790M mutation and three patients of de novo T790M mutation coexisting with L858R mutation. The incidence of de novo T790M in pretreatment NSCLCs who harboring EGFR mutations was 2.9% (4/139). All the de novo T790M mutations were detected in cis with the concomitant L858R mutations for the three NSCLCs. Our ddPCR method demonstrated that the frequency of de novo T790M mutation was ranging from 0.1% to 0.5% among 90% (45/50) of the FFPE tumor samples and 92% (46/50) of the paired FFPE adjacent normal lung samples. The frequency of de novo T790M mutation in the paired snap-frozen samples was all below 0.1%.ConclusionOur study demonstrated that most de novo T790M mutations were detected in cis with concomitant sensitizing mutations for pretreatment NSCLCs. Analytical cut-off of ddPCR assay for FFPE specimens should be validated carefully considering the possibility of FFPE-derived artificial gene mutations.

Spatially resolved analysis of FFPE tissue proteomes by quantitative mass spectrometry.

Bottom-up mass spectrometry-based proteomics relies on protein digestion and peptide purification. The application of such methods to broadly available clinical samples such as formalin-fixed and paraffin-embedded (FFPE) tissues requires reversal of chemical crosslinking and the removal of reagents that are incompatible with mass spectrometry. Here, we describe in detail a protocol that combines tissue disruption by ultrasonication, heat-induced antigen retrieval and two alternative methods for efficient detergent removal to enable quantitative proteomic analysis of limited amounts of FFPE material. To show the applicability of our approach, we used hepatocellular carcinoma (HCC) as a model system. By combining the described protocol with laser-capture microdissection, we were able to quantify the intra-tumor heterogeneity of a tumor specimen on the proteome level using a single slide with tissue of 10-µm thickness. We also demonstrate broader applicability to other tissues, including human gallbladder and heart. The procedure described in this protocol can be completed within 8 d.

Human papillomavirus is not associated to non-small cell lung cancer: data from a prospective cross-sectional study

BackgroundThe pathogenesis of lung cancer is triggered by a combination of genetic and environmental factors, being the tobacco smoke the most important risk factor. Nevertheless, the incidence of lung cancer in non-smokers is gradually increasing, which demands the search for different other etiological factors such as occupational exposure, previous lung disease, diet among others. In the early 80’s a theory linked specific types of human papillomavirus (HPV) to lung cancer due to morphological similarities of a subset of bronchial squamous cell carcinomas with other HPV-induced cancers. Since then, several studies revealed variable rates of HPV DNA detection. The current study aimed to provide accurate information on the prevalence of HPV DNA in lung cancer.MethodsBiopsies were collected from 77 newly diagnosed non-small cell lung cancer (NSCLC) patients treated at the Thoracic Oncology Department at Barretos Cancer Hospital. The samples were formalin fixed and paraffin embedded (FFPE), histologic analysis was performed by an experienced pathologist. DNA was extracted from FFPE material using a commercial extraction kit and HPV DNA detection was evaluated by multiplex PCR and HPV16 specific real-time PCR.ResultsHPV was not identified in any of the samples analysed (69).ConclusionsOur data demonstrated a lack of HPV DNA in a series of NSCL cancers.

Quantitative Profiling of Single Formalin Fixed Tumour Sections: proteomics for translational research.

Although re-sequencing of gene panels and mRNA expression profiling are now firmly established in clinical laboratories, in-depth proteome analysis has remained a niche technology, better suited for studying model systems rather than challenging materials such as clinical trial samples. To address this limitation, we have developed a novel and optimized platform called SP3-Clinical Tissue Proteomics (SP3-CTP) for in-depth proteome profiling of practical quantities of tumour tissues, including formalin fixed and paraffin embedded (FFPE). Using single 10 μm scrolls of clinical tumour blocks, we performed in-depth quantitative analyses of individual sections from ovarian tumours covering the high-grade serous, clear cell, and endometrioid histotypes. This examination enabled the generation of a novel high-resolution proteome map of ovarian cancer histotypes from clinical tissues. Comparison of the obtained proteome data with large-scale genome and transcriptome analyses validated the observed proteome biology for previously validated hallmarks of this disease, and also identified novel protein features. A tissue microarray analysis validated cystathionine gamma-lyase (CTH) as a novel clear cell carcinoma feature with potential clinical relevance. In addition to providing a milestone in the understanding of ovarian cancer biology, these results show that in-depth proteomic analysis of clinically annotated FFPE materials can be effectively used as a biomarker discovery tool and perhaps ultimately as a diagnostic approach.

Single-strand DNA library preparation improves sequencing of formalin-fixed and paraffin-embedded (FFPE) cancer DNA.

DNA derived from formalin-fixed and paraffin-embedded (FFPE) tissue has been a challenge to large-scale genomic sequencing, due to its low quality and quantities. Improved techniques enabling the genome-wide analysis of FFPE material would be of great value, both from a research and clinical perspective.Comparing a single-strand DNA library preparation method originally developed for ancient DNA to conventional protocols using double-stranded DNA derived from FFPE material we obtain on average 900-fold more library molecules and improved sequence complexity from as little as 5 ng input DNA. FFPE DNA is highly fragmented, usually below 100bp, and up to 60% of reads start after or end prior to adenine residues, suggesting that crosslinks predominate at adenine residues. Similar to ancient DNA, C > T substitutions are slightly increased with maximum rates up to 3% at the ends of molecules. In whole exome sequencing of single-strand libraries from lung, breast, colorectal, prostate and skin cancers we identify known cancer mutations. In summary, we show that single-strand library preparation enables genomic sequencing, even from low amounts of degraded FFPE DNA. This method provides a clear advantage both in research and clinical settings, where FFPE material (e.g. from biopsies) often is the only source of DNA available. Improving the genetic characterization that can be performed on conventional archived FFPE tissue, the single-strand library preparation allows scarce samples to be used in personalized medicine and enables larger sample sizes in future sequencing studies.

Identification by FFPE RNA-Seq of a new recurrent inversion leading to RBM10-TFE3 fusion in renal cell carcinoma with subtle TFE3 break-apart FISH pattern.

Gene fusions involving TFE3 defines the "Xp11.2 translocations" subclass of renal cell carcinomas (RCCs) belonging to the MiT family translocation RCC. Four recurrent TFE3 fusion partners were identified to date: PRCC, ASPSCR1, SFPQ, and NONO. Break-apart TFE3 fluorescence in situ hybridization (FISH) on formalin-fixed and paraffin-embedded (FFPE) tissue sections is currently the gold standard for identification of TFE3 rearrangements. Herein, we report a case of RCC with a morphological appearance of Xp11.2 translocation, and positive TFE3 immunostaining. By FISH, the spots constituting the split signal were barely spaced, suggestive of a chromosome X inversion rather than a translocation. We performed RNA-seq from FFPE material to test this hypothesis. RNA-seq suggested a fusion of RBM10 gene exon 17 (Xp11.23) with TFE3 gene exon 5 (Xp11.2). RBM10-TFE3 fusion transcript was confirmed using specific RT-PCR. Our work showed that RNA-Seq is a robust technique to detect fusion transcripts from FFPE material. A RBM10-TFE3 fusion was previously described in single case of Xp11.2 RCC. Although rare, RBM10-TFE3 fusion variant (from chromosome X paracentric inversion), therefore, appears to be a recurrent molecular event in Xp11.2 RCCs. RBM10-TFE3 fusion should be added in the list of screened fusion transcripts in targeted molecular diagnostic multiplex RT-PCR. © 2016 Wiley Periodicals, Inc.

First report of a novel pigmented Mycobacterium sp. causing a cluster of post-laparotomy wound infections from India

The clinical, histologic, and radiographic presentations of nontuberculous mycobacterial (NTM) lung disease are usually indistinguishable from those of reactivated pulmonary tuberculosis (TB), so it remains a great challenge for the clinician to make treatment decisions for patients with old TB and a positive culture result for NTM. This study investigated whether the mycobacterial specific heat shock protein 65 (hsp65) and Mycobacterium tuberculosis (MTB)-specific IS6110 gene would present in pulmonary lesions of patients with NTM pulmonary infection. Formalin-fixed and paraffin-embedded (FFPE) tissue blocks of 24 patients with NTM infections treated at the hospital from 1998 to 2008 were included. Mycobacterial hsp65 gene was amplified in 20 of the 24 patients, and the species identified by sequencing was consistent with corresponding culture results in 12 of these patients. MTB-specific IS6110 gene was detected in 3 of the 7 patients who had old TB and a subsequent diagnosis of fibrocavitary NTM lung disease. Polymerase chain reaction (PCR) analysis of hsp65 gene also confirmed the presence of MTB genes in 2 of these 3 patients. Our results indicate that PCR amplification and sequencing of the mycobacterial hsp65 gene is a sensitive assay for identification of NTM species in FFPE materials. However, consistent results of PCR analysis, microbiology study, histologic manifestations, radiology, and clinical presentation are important for correct diagnosis of NTM pulmonary infection. The presence of MTB gene in patients with fibrocavitary NTM lung lesions poses a clinical dilemma for deciding concurrent treatment TB and NTM infection.

Proteomic Sample Preparation from Formalin Fixed and Paraffin Embedded Tissue

Preserved clinical material is a unique source for proteomic investigation of human disorders. Here we describe an optimized protocol allowing large scale quantitative analysis of formalin fixed and paraffin embedded (FFPE) tissue. The procedure comprises four distinct steps. The first one is the preparation of sections from the FFPE material and microdissection of cells of interest. In the second step the isolated cells are lysed and processed using 'filter aided sample preparation' (FASP) technique. In this step, proteins are depleted from reagents used for the sample lysis and are digested in two-steps using endoproteinase LysC and trypsin. After each digestion, the peptides are collected in separate fractions and their content is determined using a highly sensitive fluorescence measurement. Finally, the peptides are fractionated on 'pipette-tip' microcolumns. The LysC-peptides are separated into 4 fractions whereas the tryptic peptides are separated into 2 fractions. In this way prepared samples allow analysis of proteomes from minute amounts of material to a depth of 10,000 proteins. Thus, the described workflow is a powerful technique for studying diseases in a system-wide-fashion as well as for identification of potential biomarkers and drug targets.

Proteomic Sample Preparation from Formalin Fixed and Paraffin Embedded Tissue

Preserved clinical material is a unique source for proteomic investigation of human disorders. Here we describe an optimized protocol allowing large scale quantitative analysis of formalin fixed and paraffin embedded (FFPE) tissue. The procedure comprises four distinct steps. The first one is the preparation of sections from the FFPE material and microdissection of cells of interest. In the second step the isolated cells are lysed and processed using 'filter aided sample preparation' (FASP) technique. In this step, proteins are depleted from reagents used for the sample lysis and are digested in two-steps using endoproteinase LysC and trypsin. After each digestion, the peptides are collected in separate fractions and their content is determined using a highly sensitive fluorescence measurement. Finally, the peptides are fractionated on 'pipette-tip' microcolumns. The LysC-peptides are separated into 4 fractions whereas the tryptic peptides are separated into 2 fractions. In this way prepared samples allow analysis of proteomes from minute amounts of material to a depth of 10,000 proteins. Thus, the described workflow is a powerful technique for studying diseases in a system-wide-fashion as well as for identification of potential biomarkers and drug targets.

Detection of immunoglobulins and complement components in formalin fixed and paraffin embedded renal biopsy material by immunoflourescence technique

The technique of direct immunoflourescence (IF) is essential in the accurate diagnosis of renal glomerular diseases. The optimal results are obtained when the procedure is done on fresh frozen tissue (IF-F). However, techniques are available for IF study on formalin fixed and paraffin embedded (FFPE) renal biopsy specimens with variable reported success rates. We evaluated three such techniques on FFPE tissue and compared the results with those obtained by IF-F from the same patients. Heat treatment with Tris buffer and citrate buffer, and pronase treatment of the FFPE material was carried out. Direct IF was done for renal panel immunoglobulins and complement components on all biopsies and the results were compared with the historical IF-F study. When compared to the IF-F, the immunoflourescence staining on the paraffin sections was less sensitive and less intense in all immune complex-mediated renal diseases, but the diagnostic findings were detected in majority of the cases. In conclusion, it is possible to establish the diagnosis in most cases of immune complex-mediated glomerular diseases with IF on paraffin embedded tissue specimens.

Comparison of Formalin-Fixed and Snap-Frozen Samples Analyzed by Multiplex Ligation-Dependent Probe Amplification for Prognostic Testing in Uveal Melanoma

Survival of patients with uveal melanoma (UM) correlates strongly with chromosomal abnormalities, such as monosomy 3 and polysomy 8q. Studies have shown multiplex ligation-dependent probe amplification (MLPA) to detect reliably chromosomal aberrations in UM using frozen samples. To date, the concordance between MLPA data generated from frozen and fixed samples has not been investigated. Our study aimed to compare MLPA data obtained from fixed and frozen tissues to determine whether fixed samples can be used in UM genetic prognostic testing. Adjacent samples were taken from 20 UM cases, with one sample being snap-frozen, and the second being formalin-fixed and paraffin-embedded (FFPE). MLPA analysis was performed using the P027.B1 assay. The chromosome arm copy numbers obtained for each pair of UM samples then were compared. Of the 20 UM cases 18 gave MLPA results from FFPE material that passed quality control thresholds. When chromosome 3 copy number was classified successfully (loss, disomy or gain) using FFPE material, the corresponding frozen sample showed concordance in 100% of cases. However, even when FFPE samples passed quality thresholds, chromosome arm copy numbers for 3p and 3q were "unclassifiable" in 28% and 11% of cases, respectively. This compared to "unclassifiable" cases in 0% and 6% of the frozen UM samples. Whenever possible, fresh or snap-frozen tissue should be used for UM genetic prognostic testing by MLPA. When only fixed tissue is available, MLPA can be used to determine reliably chromosome 3 copy number. However, some tumors will be unclassifiable where DNA quality is poor.

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.

Identification of nontuberculous mycobacterial infection by IS6110 and hsp65 gene analysis on lung tissues

The clinical, histologic, and radiographic presentations of nontuberculous mycobacterial (NTM) lung disease are usually indistinguishable from those of reactivated pulmonary tuberculosis (TB), so it remains a great challenge for the clinician to make treatment decisions for patients with old TB and a positive culture result for NTM. This study investigated whether the mycobacterial specific heat shock protein 65 (hsp65) and Mycobacterium tuberculosis (MTB)-specific IS6110 gene would present in pulmonary lesions of patients with NTM pulmonary infection. Formalin-fixed and paraffin-embedded (FFPE) tissue blocks of 24 patients with NTM infections treated at the hospital from 1998 to 2008 were included. Mycobacterial hsp65 gene was amplified in 20 of the 24 patients, and the species identified by sequencing was consistent with corresponding culture results in 12 of these patients. MTB-specific IS6110 gene was detected in 3 of the 7 patients who had old TB and a subsequent diagnosis of fibrocavitary NTM lung disease. Polymerase chain reaction (PCR) analysis of hsp65 gene also confirmed the presence of MTB genes in 2 of these 3 patients. Our results indicate that PCR amplification and sequencing of the mycobacterial hsp65 gene is a sensitive assay for identification of NTM species in FFPE materials. However, consistent results of PCR analysis, microbiology study, histologic manifestations, radiology, and clinical presentation are important for correct diagnosis of NTM pulmonary infection. The presence of MTB gene in patients with fibrocavitary NTM lung lesions poses a clinical dilemma for deciding concurrent treatment TB and NTM infection.

Fixation of Brain Tumor Biopsy Specimens with RCL2 Results in Well‐Preserved Histomorphology, Immunohistochemistry and Nucleic Acids

RCL2 is an alcohol-based fixative reported to preserve histomorphology and nucleic acids in non-CNS neoplasms. We compared histomorphology, immunohistochemistry, DNA and RNA in brain tumor specimens preserved frozen at -80°C, and after formalin or RCL2 fixation. RCL2-fixed and paraffin-embedded (RCLPE) samples showed well-preserved histomorphology and specific immunoreactivity comparable to formalin-fixed and paraffin-embedded (FFPE) specimens testing a broad panel of antibodies. In all the analyzed cases, high-molecular weight DNA (up to a fragment length of 600 bp) was amplifyable from RCLPE samples, even after prolonged fixation times. Beta-actin (ACTB) and O6-methylguanine-methyltransferase (MGMT) gene concentrations were significantly higher in DNA isolated from RCLPE specimens as compared with FFPE specimens. Testing of MGMT promoter methylation status using methylation-specific polymerase-chain reaction (MSP) yielded conclusive results in 8/8 analyses in RCLPE and 6/8 analyses in FFPE material, respectively. Amplification of three reference genes (ABL, RAR-alpha, BCR-1) from cDNA showed good RNA preservation in frozen and RCLPE tissue specimens and significant RNA degradation in all FFPE samples. In conclusion, RCL2 fixation of brain tumor biopsies does not seem to significantly compromise histological tumor typing or immunohistochemistry and preserves nucleic acids (DNA and RNA) at a better quality than formalin fixation.

MicroRNA Expression in Melanocytic Nevi: The Usefulness of Formalin-Fixed, Paraffin-Embedded Material for miRNA Microarray Profiling

MicroRNAs (miRNAs) are small, noncoding RNA molecules that regulate cellular differentiation, proliferation, and apoptosis. MiRNAs are expressed in a developmentally regulated and tissue-specific manner. Aberrant expression may contribute to pathological processes such as cancer, and miRNA may therefore serve as biomarkers that may be useful in a clinical environment for diagnosis of various diseases. Most miRNA profiling studies have used fresh tissue samples. However, in some types of cancer, including malignant melanoma, fresh material is difficult to obtain from primary tumors, and most surgical specimens are formalin fixed and paraffin embedded (FFPE). To explore whether FFPE material would be suitable for miRNA profiling in melanocytic lesions, we compared miRNA expression patterns in FFPE versus fresh frozen samples, obtained from 15 human melanocytic nevi. Out of microarray data, we identified 84 miRNAs that were expressed in both types of samples and represented an miRNA profile of melanocytic nevi. Our results showed a high correlation in miRNA expression (Spearman r-value of 0.80) between paired FFPE and fresh frozen material. The data were further validated by quantitative RT-PCR. In conclusion, FFPE specimens of melanocytic lesions are suitable as a source for miRNA microarray profiling.

Global gene expression profiling of formalin-fixed paraffin-embedded tumor samples: a comparison to snap-frozen material using oligonucleotide microarrays

Oligonucleotide microarrays are widely used to investigate gene expression in a large-scale approach. A major limitation is the dependency on frozen material to obtain high-quality ribonucleic acid because most clinical specimens are formalin-fixed and paraffin-embedded (FFPE). The ability to analyze these samples using microarrays would enlarge the investigable sample stocks manifold. We conducted a comparison of snap-frozen and FFPE tissues investigating two malignomas. Gene expression profiles were obtained from both materials of the tumors. Independently processed triplicates of snap-frozen and FFPE specimen, respectively, were two-round-amplified and hybridized on Affymetrix GeneChips (Palo Alto, CA, USA). Differentially expressed genes were identified in both FFPE and frozen material. All replicates had a correlation coefficient (R) of greater than 0.95 after normalization. Only direct comparison of FFPE to frozen replicates resulted in a mean R of 0.86, rendering a "mixed" investigation unfeasible. More than 50% (419 genes) of the more than fivefold differentially expressed genes (800 in FFPE, 685 in frozen material) were detected concomitantly regardless of the material used, which is similar to other comparisons of different gene expression analysis platforms. Thus, global gene expression analyses using solely FFPE material seem to be feasible with nearly comparable results to frozen tissue studies.