Panfungal PCR on formalin-fixed, paraffin-embedded tissue: to proceed or not proceed?

Performance of panfungal PCR-DNA sequencing assays for diagnosis of invasive fungal disease on formalin-fixed, paraffin-embedded tissue (FFPE) is influenced by many variables. Interpretation of a positive result can be challenging due to the need to differentiate colonisers and contaminants from clinically significant pathogens. We conducted a retrospective audit on FFPE tissue specimens that underwent panfungal PCR from January 2021 to August 2022. Panfungal PCR results from samples where fungal elements were visualised on histopathology were compared with results from samples where no fungal elements were visualised. The cost per clinically significant positive sample in each group was calculated. Of the 248 FFPE tissues sampled, 18.1% (45/248) had fungal forms seen on histopathology. Panfungal PCR was positive in 22/45 samples (48.9%), with 16 (35.6%) results deemed clinically significant. For the remaining 203 specimens, panfungal PCR was positive in 19 (9.4%) samples with only six (3.0%) clinically significant. The average cost per clinically significant result was AUD 258.13 in the histopathology positive group and AUD 3,105.22 in the histopathology negative group. Our data suggest panfungal PCR has limited clinical utility in FFPE tissue when no fungal elements are seen. Restricting the assay to only those samples that are positive on histopathological examination aids interpretation of PCR positive results and conserves laboratory resources.

The effectiveness of various strategies to improve DNA analysis of formaldehyde-damaged tissues from embalmed cadavers for human identification purposes

Formalin-fixed tissues provide the medical and forensic communities with alternative and often last resort sources of DNA for identification or diagnostic purposes. The DNA in these samples can be highly degraded and chemically damaged, making downstream genotyping using short tandem repeats (STRs) challenging. Therefore, the use of alternative genetic markers, methods that pre-amplify the low amount of good quality DNA present, or methods that repair the damaged DNA template may provide more probative genetic information. This study investigated whether whole genome amplification (WGA) and DNA repair could improve STR typing of formaldehyde-damaged (FD) tissues from embalmed cadavers. Additionally, comparative genotyping success using bi-allelic markers, including INDELs and SNPs, was explored. Calculated random match probabilities (RMPs) using traditional STRs, INDEL markers, and two next generation sequencing (NGS) panels were compared across all samples. Overall, results showed that neither WGA nor DNA repair substantially improved STR success rates from formalin-fixed tissue samples. However, when DNA from FD samples was genotyped using INDEL and SNP-based panels, the RMP of each sample was markedly lower than the RMPs calculated from partial STR profiles. Therefore, the results of this study suggest that rather than attempting to improve the quantity and quality of severely damaged and degraded DNA prior to STR typing, a more productive approach may be to target smaller amplicons to provide more discriminatory DNA identifications. Furthermore, an NGS panel with less loci may yield better results when examining FD samples, due to more optimized chemistries that result in greater allelic balance and amplicon coverage.

[Extraction and isolation of histones from paraffin-embedded tissues and quantitative analysis of post-translational modifications]

Histone post-translational modifications (HPTMs) have been believed to play crucial roles in the regulation of gene transcription. Thus, aberrant modification of histone can contribute to the occurrence and development of diseases such as tumors. To date, formalin fixed paraffin-embedded (FFPE) clinical tissues are believed to be one of the most valuable sample resources in the study of human diseases. Therefore, it is of great significance to reveal the molecular mechanism of cancer and discover the markers of tumor. Proteomics, based on high performance liquid chromatograph-tandem mass spectrometry (HPLC-MS/MS), has become a powerful tool for HPTM identification. However, HPTM analysis of FFPE samples is yet to be explored; it has not been reported in China to our best knowledge. In this study, a new method based on HPLC-MS/MS was developed for the extraction and separation of histone proteins and analysis and quantification of HPTMs in FFPE tissues. First, the strategy for the extraction and separation of histone proteins from FFPE samples were optimized. After comparing the extraction efficiency of two different methods, which include the acid extraction of histone and extraction of total protein, a novel method was developed for histone extraction, separation, and HPTMs analysis by integrating dewaxed hydration treatment of FFPE tissues with protein extraction and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) separation. Furthermore, the effects of operation parameters on histone extraction and HPTM identification were investigated, including number of paraffin embedded sections and chemical derivation of histone proteins. Thereafter, the identification and quantification of HPTMs were performed using reversed-phase HPLC-MS/MS in data independent acquisition (DIA) mode. Finally, the optimized methods were applied to quantitative analysis of HPTMs in FFPE tissues. A variety of HPTMs were identified; they included lysine methylation, acetylation, crotonylation, etc. Therefore, the spectrum of HPTMs on global level was set for human breast cancer and paracancerous tissues from two cases of FFPE clinical tissues. The sites holding differential HPTM level in cancer and paracancerous tissues were further obtained by quantifying the individual HPTMs. Thus, the relationship between HPTM level and tumor was discussed. Abnormal HPTM sites were characterized using cluster analysis, thus their similar tendency was found. For example, abnormal HPTM sites such as H3K9me3, H3K9ac, and H3K27me3 in cancers are associated with epigenetic regulation. It indicated that different epigenetic events might occur in cancer and paracancerous tissues. Interestingly, we found that the level of H4K20me3 were both significantly down-regulated in the two cancer tissues. HPTM had been thought to be a potential biomarker in breast cancer; therefore, these positive results indicated that our method is effective for HPTMs of clinical FFPE samples. Our study provides a useful tool for the isolation and analysis of HPTMs in clinical FFPE samples, showing the potential for the detection of epigenetic biomarker in cancer.

Performance evaluation of fungal DNA PCR amplification from formalin-fixed paraffin-embedded tissue for diagnosis: Experience of a tertiary reference laboratory

BACKGROUND

Diagnosis of invasive fungal infections from formalin-fixed paraffin-embedded (FFPE) tissues by PCR amplification is a developing technology. One of the difficulties of establishing a validated protocol for this testing is that the gold standard, culture, is much less sensitive than the test being validated.

OBJECTIVES

To validate FFPE PCR as a refence laboratory identification methodology in the absence of abundant gold standard specimens.

METHODS

In this validation, PCR from FFPE tissue was compared to other diagnostic methods for genus/species identification. Four different groups of correlative data from FFPE tissues were used to validate this procedure. Thirteen specimens had culture or serology results and FFPE PCR results, 49 specimens had both immunohistochemistry (IHC) identification and FFPE PCR results, 118 specimens had histological evidence of fungal elements, 64 of which also had FFPE PCR results, and 36 fungal mock tissues or fungal negative tissues were used.

RESULTS

The sensitivity determined from the tissues with positive fungal histopathology was 54%. The specificity of the cases for which there were both culture and FFPE PCR results was 100%. For the correlation with IHC, the specificity was 98%. For the mock tissues and fungal negative tissues, the calculated analytical sensitivity was 94%, specificity was 95%, and accuracy was 94%.

CONCLUSIONS

By uniquely combining various data sources, this study provides a comprehensive framework for how validation can be achieved in the absence of a gold standard and outlines the excellent performance of PCR from FFPE tissue, despite relatively the low sensitivity when compared to histopathology.

Luminex-based quantification of Alzheimer's disease neuropathologic change in formalin-fixed post-mortem human brain tissue

The vast majority of archived research and clinical pathological specimens are stored in the form of formalin fixed, paraffin-embedded (FFPE) tissues, but, unlike fresh frozen tissue samples, highly quantitative measures in FFPE tissues are limited to immunohistochemical and immunofluorescence thresholding image analysis studies, cell counting, and ordinal ranking systems. This poses a significant obstacle for clinical investigations that aim to correlate diagnostic markers of neurodegenerative diseases like Alzheimer's disease (AD) with parameters like age, gender, drug exposures, genotype, disease stage, co-morbidities, or environmental factors. To overcome this limitation, we have developed Luminex-based techniques and protocols for the quantification of amyloid β and hyperphosphorylated Tau in FFPE brain sections. We validated the Luminex assay in FFPE sections from prefrontal cortex, hippocampus, and neostriatum from 30 cases that underwent prior neuropathological diagnostic assessment of AD following the current NIA-AA recommendations for AD: 10 cases diagnosed as not or low, 10 cases as intermediate, and 10 cases as high AD neuropathologic change. Consistent with the neuropathologic assessment, Luminex assay detected high amounts of amyloid beta in the frontal cortex and striatum, and high amounts of hyperphosphorylated Tau in the frontal cortex and hippocampus, of cases with high AD neuropathologic change. This assay can be expanded to detect diverse antigenic targets of interest, as we show here with IBA1 and GFAP. This novel approach supports multiplexed highly quantitative, molecularly specific neuropathology measures to further explore mechanisms of neurodegeneration in AD.

Detection of the BRAF V600E Mutation in Colorectal Cancer by NIR Spectroscopy in Conjunction with Counter Propagation Artificial Neural Network

This paper proposes a sensitive, sample preparation-free, rapid, and low-cost method for the detection of the B-rapidly accelerated fibrosarcoma (BRAF) gene mutation involving a substitution of valine to glutamic acid at codon 600 (V600E) in colorectal cancer (CRC) by near-infrared (NIR) spectroscopy in conjunction with counter propagation artificial neural network (CP-ANN). The NIR spectral data from 104 paraffin-embedded CRC tissue samples consisting of an equal number of the BRAF V600E mutant and wild-type ones calibrated and validated the CP-ANN model. As a result, the CP-ANN model had the classification accuracy of calibration (CAC) 98.0%, cross-validation (CACV) 95.0% and validation (CAV) 94.4%. When used to detect the BRAF V600E mutation in CRC, the model showed a diagnostic sensitivity of 100.0%, a diagnostic specificity of 87.5%, and a diagnostic accuracy of 93.8%. Moreover, this method was proven to distinguish the BRAF V600E mutant from the wild type based on intrinsic differences by using a total of 312 CRC tissue samples paraffin-embedded, deparaffinized, and stained. The novel method can be used for the auxiliary diagnosis of the BRAF V600E mutation in CRC. This work can expand the application of NIR spectroscopy in the auxiliary diagnosis of gene mutation in human cancer.

Extraction of RNA from formalin-fixed, paraffin-embedded equine placenta

Archived formalin-fixed, paraffin-embedded (FFPE) samples represent a valuable resource for the determination of gene expression for physio/pathological conditions. In the present study, we validated a protocol for the extraction of RNA from FFPE samples collected from healthy and diseased equine placenta. The quality and quantity of the extracted RNA from the FFPE and matching RNAlater™-preserved samples and expression levels of common housekeeping genes and reference microRNAs were evaluated. Precision of the expression data was evaluated by comparing relative expression of CYP19A1 and HSD3B1 in FFPE and RNAlater™ samples. The median RNA concentration recovered from FFPE samples was 316.8 ng/mm³ of tissue (ranging between 61.6 and 917.4 ng/mm³ ), average RNA integrity number was 2.3 ± 0.9 (mean ± standard deviation), and 84% of samples had RNA fragments longer than 200 nucleotides (DV₂₀₀ ). RNA concentrations and C_T values for GAPDH, ACTB, miR-8908a and miR-369 in FFPE samples were significantly correlated (r = -0.8, -0.7, -0.4 and -0.4, respectively; p < 0.001). Expression pattern of normalized CYP19A1 and HSD3B1 in paired FFPE and RNAlater™ samples was significantly correlated (r = 0.97 for CYP19A1 and HSD3B1; p < 0.001). This study demonstrates that RNA can be extracted from FFPE equine placental tissue and used for downstream transcriptomic analysis. Similar RNA expression patterns were obtained using RNAlater™ and FFPE tissue samples.

Stability of oestrogen and progesterone receptor antigenicity in formalin-fixed paraffin-embedded breast cancer tissue over time

Use of archived formalin-fixed paraffin-embedded (FFPE) tissue is a standard method for evaluation of proposed prognostic and predictive tumour markers. However, little is known of the preservation of biomarker expression in old FFPE tumour blocks. We investigate the quality of immunohistochemical (IHC) oestrogen (ER) and progesterone receptor (PR) evaluation in FFPE tissue over time (1978-2000) using a large breast cancer tissue microarray (N = 573) with access to receptor analyses in cytosol (CYT) at diagnosis, coexpression of other biomarkers and follow-up data. We found a good correlation between ER analysed with CYT at diagnosis and ER analysed with IHC in archived FFPE tissue from the same tumour. ER evaluation did not seem to be affected by tissue storage time. Nor was there any time-dependent difference in ER_IHC correlation with other biomarkers (HER2, Ki67) or survival. Discordant cases were more often classified as ER-positive with IHC than with CYT. For PR, however, we found an increased correlation between methods in more recent time periods. This may possibly be explained by more reliable PR_IHC results in newer samples, although other explanations may also contribute. Our results indicate stable ER expression in FFPE tissue archived for up to 40 years.

FNA smears of pancreatic ductal adenocarcinoma are superior to formalin-fixed paraffin-embedded tissue as a source of DNA: Comparison of targeted KRAS amplification and genotyping in matched preresection and postresection samples

BACKGROUND

The current study was conducted to compare DNA yield, including normalization to nuclear area, DNA amplification functionality, and detection of KRAS mutations between matched fine-needle aspiration (FNA) specimens and pancreatic resections diagnostic of pancreatic ductal adenocarcinoma.

METHODS

A retrospective sample of 30 matched single FNA smears and macrodissected formalin-fixed, paraffin-embedded (FFPE) curls (2 5-μm curls) were compared by measuring the following: nuclear area (via digital image analysis), DNA yield (via NanoDrop spectrophotometry and Quantus fluorometry), and polymerase chain reaction threshold cycles for KRAS amplifications. Variants in KRAS codons 12/13 and 61 were detected by fluorescent melt curve analyses, followed by Sanger DNA sequencing.

RESULTS

Despite a similar nuclear area, FNA smears yielded greater DNA per nuclear area via 2 DNA quantification methods. KRAS codon 12 mutations were detected in 23 of 30 FNA specimens (77%) compared with 17 of 30 matched FFPE specimens (57%), for a concordance rate of 74%. No KRAS codon 13 or 61 mutations were detected.

CONCLUSIONS

FNA specimens are a more optimal source of DNA, and represent an important resource in the preresection and postresection molecular analysis of pancreatic ductal adenocarcinoma. Cancer Cytopathol 2017;125:838-47. © 2017 American Cancer Society.

Comparison of Five Commercial Nucleic Acid Extraction Kits for the PCR-based Detection of Burkholderia Pseudomallei DNA in Formalin-Fixed, Paraffin-Embedded Tissues

The extraction and further processing of nucleic acids (NA) from formalin-fixed paraffin-embedded (FFPE) tissues for microbiological diagnostic polymerase chain reaction (PCR) approaches is challenging. Here, we assessed the effects of five different commercially available nucleic acid extraction kits on the results of real-time PCR.

FFPE samples from organs of Burkholderia pseudomallei-infected Swiss mice were subjected to processing with five different extraction kits from QIAGEN (FFPE DNA Tissue Kit, EZ1 DNA Tissue Kit, DNA Mini Kit, DNA Blood Mini Kit, and FlexiGene DNA Kit) in combination with three different real-time PCRs targeting B. pseudomallei-specific sequences of varying length after 16 years of storage.

The EZ1 DNA Tissue Kit and the DNA Mini Kit scored best regarding the numbers of successful PCR reactions. In case of positive PCR, differences regarding the cycle-threshold (Ct) values were marginal.

The impact of the applied extraction kits on the reliability of PCR from FFPE material seems to be low. Interfering factors like the quality of the dewaxing procedure or the sample age appear more important than the selection of specialized FFPE kits.

The paraffin-embedded RNA metric (PERM) for RNA isolated from formalin-fixed, paraffin-embedded tissue

RNA isolated from formalin-fixed, paraffin-embedded (FFPE) tissue is commonly evaluated in both investigative and diagnostic pathology. However, the quality of the data is directly impacted by RNA quality. The RNA integrity number (RIN), an algorithm based on a combination of electrophoretic features, is widely applied to RNA isolated from paraffin-embedded tissue, but it is a poor indicator of the quality of that RNA. Here we describe the novel paraffin-embedded RNA metric (PERM) for quantifying the quality of RNA from FFPE tissue. The PERM is based on a formula that approximates a weighted area-under-the-curve analysis of an electropherogram of the extracted RNA. Using biochemically degraded RNAs prepared from experimentally fixed mouse kidney specimens, we demonstrate that PERM values correlate with mRNA transcript measurements determined using the QuantiGene system. Furthermore, PERM values correlate with real-time PCR data. Our results demonstrate that the PERM can be used to qualify RNA for different end-point studies and may be a valuable tool for molecular studies using RNA extracted from FFPE tissue.