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

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.