Quality assessment of long-term stored formalin-fixed paraffin embedded tissues for histopathological evaluation

Abstract

Histopathological examination of formalin-fixed paraffin-embedded (FFPE) tissues that had been stored for 30 years was conducted, and reconstructivity of the results was verified. These FFPE tissues, which were from all organs of male and female rats, were re-sectioned and histopathologically examined using hematoxylin and eosin (HE) staining. In particular, the stainability and morphology of HE sections and reproducibility of microscopic findings in the liver and kidney demonstrated in the original final reports were evaluated. Although the stainability of hematoxylin was slightly weaker and some morphological artifacts were observed in tissues in re-prepared slides, these deteriorations in the quality of HE sections were considered to be permissible for histopathological examination so long as control sections were also prepared. Most microscopic findings recorded in the original final reports were confirmed using re-prepared HE sections in the present study. While some focal findings, which were judged to be either incidental or spontaneous in nature, were not observed in the sections as expected, this was not considered to be a problem in reconstructing the results of the original histopathological examination because most findings related to the test articles were generally observed diffusely or multifocally in each organ. We concluded that results of the original histopathological examinations could be reconstructed using paraffin blocks that had been stored for up to 30 years. Appropriate archiving of records and materials generated in good laboratory practice (GLP) studies is required to comply with the principles of GLP 1 . This is because the maintenance of raw data associated with a specific study and the specimens generated from that study are the only means that can be used to reconstruct the study. In several countries, the retention period for specimens of a GLP study is set such that it expires when they can no longer be evaluated. Consequently, formalin-fixed organs, paraffin-embedded blocks, and hematoxylin and eosin (HE)-stained slides have been stored for long periods in each test facility.The quality of long-term stored formalin-fixed wet tissues has been histopathologically evaluated by producing HE sections 2-4 . To the best of our knowledge, no studies have reported the quality evaluation of long-term stored formalin-fixed paraffin-embedded (FFPE) tissues. Here we re-prepared HE sections from FFPE tissues that had been previously stored for approximately 30 years and histopathologically evaluated the quality of these tissues and reproducibility of microscopic findings. We then investigated the possibility of reconstructing the results of the original histopathological examination using re-prepared HE sections from long-term stored paraffin blocks.This study evaluated FFPE tissues that had been stored for approximately 30 years. FFPE blocks evaluated in this study contained all the organs of 4 males and 4 females, i.e., 1 or 2 males and females each from three GLP toxicity studie...

Comparison of staining adequacy between tissues stored in formalin and paraffin embedded blocks for prolonged duration

“…Quality of formalin fixed tissues stored for 30 years in rat specimen for histopathological analysis reported fading in staining and few morphological artifacts and concluded that their results were favorable and comparable to their original histopathological reports. [ 8 ]…”

“…This reduction in staining quality in LFT from our study can be related to stainability and microscopic findings in liver, kidney and other organs assessed in rat tissues that were stored for 30 years. [ 8 ] Less satisfactory staining of prolonged formalin-fixed tissues than paraffin embedded blocks is due to excessive cross-linking of proteins and production of formic acid which lowers the pH of formalin fixative solution in which tissues are preserved for prolonged duration. Staining adequacy of the tissue sections for H&E, was found to be superior as compared to Mallory's stain and Van Gieson's stain.…”

The Use of Digital Microscopy to Compare the Thicknesses of Normal Corneas and Ex Vivo Rejected Corneal Grafts with a Focus on the Descemet’s Membrane

“…It is also important to note that the tissues can be affected by different factors at the time of preparation of the samples. Tissue manipulation during surgery, formalin fixation, paraffin embedment, and storage methods are conditions that impact the quality of the histological specimen [29, 30], which could limit the improvement of histopathological studies.…”

Tumor Pre-Analytics in Molecular Pathology: Impact on Protein Expression and Analysis

“…At the same time, the quality of FFPE biospecimens, often stored over a long-term period, needs to be critically evaluated to determine their fit-for-purpose for accurate molecular phenotyping. While formalin fixation and paraffin embedding preserves tissue morphology for up to 30 years of storage [ 90 ], including cytological details and immune-reactivity of tissue antigens, recent studies investigate the influence of long-term storage on complex molecular analytes. Results, however, are somehow controversial with studies concluding that the fitness of FFPE blocks for proteomic analysis is independent of tissue age evaluating a time frame of 11 years [ 91 ], respectively 11-year intervals from 1990 to 2001 and from 2002 to 2013 [ 92 ], but rather dependent on tissue and tumor type, reporting significant differences in protein derivatives between papillary, squamous, and adenocarcinomas as measured by protein absorbance values in one of the studies [ 92 ].…”