Cancer Diagnosis Program | Biorepositories and Biospecimen Research Branch

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Evaluation of methods for preserving PTEN antigenicity in stored paraffin sections.

Author(s): Gelb AB, Freeman VA, Astrow SH

Publication: Appl Immunohistochem Mol Morphol, 2011, Vol. 19, Page 569-73

PubMed ID: 21552118 PubMed Review Paper? No

Purpose of Paper

Conclusion of Paper

Studies

1. Study Purpose

   This study examined the stability of PTEN antigenicity in slide-mounted paraffin sections that were coated in paraffin or left unaltered prior to storage for 2 to 6 months at room temperature or 4°C compared to those analyzed immediately. Freshly cut sections from 26 cases of breast carcinoma specimens were mounted on slides and either left unaltered or dipped in paraffin (60°C) and cooled.  Subsets of each type of slide were then stored protected from light in plastic slide boxes at room temperature (20-25°C) or 4-8°C for 2, 4, and 6 months.  Freshly cut and stored sections were analyzed by immunohistochemistry for PTEN after antigen retrieval (incubation in modified citrate buffer in a pressure cooker). Immunostaining was assessed by a single pathologist and quantified by histoscore, which considered both the percentage of stained cells as well as the intensity of staining. Cells were considered positive if immunostaining was present in the cytoplasm and/or nucleus of the tumor cell. The authors noted that a 25% decline in histoscore was assigned as a threshold for loss of antigenicity to minimize the occurrence of false-positives. Information on how specimens were fixed and processed were not provided. Statistical significance was set at 0.05 and was determined by the nonparametric Kruskal-Wallis and Dunn's multiple comparison tests and Wilcoxon signed rank test.

   Summary of Findings:

   The analysis of effects of slide storage on the stability of PTEN antigenicity was limited to the 19 of 26 cases of breast carcinoma that were positive for PTEN expression. When slides were stored unaltered at room temperature, PTEN histoscores declined by 50% after 2 months (P=0.034) and 75% after 4 months (P<0.0001) compared to those analyzed immediately after sectioning.  PTEN histoscores were significantly higher when slides were coated in paraffin and stored at 4°C compared to unaltered slides stored at room temperature (P=0.0016). However, loss of PTEN antigenicity was observed among paraffin-coated slides after 6 months of storage at 4°C, as histoscores declined by 56% compared to those analyzed immediately after sectioning.  Although exact percentages were not noted, storage of unaltered slides at 4°C produced comparable histoscores to those coated in paraffin after 2 months of storage but much lower scores (20 vs 60) after 4 months and storage of paraffin-coated slides at room temperature produced suboptimal results after 2 and 4 months of storage.  The authors conclude that PTEN antigenicity remains stable for up to 2 months when unaltered slides are stored at 4°C and for up to 4 months when paraffin-coated slides are stored at 4°C.

   Biospecimens

   • Tissue - Breast

   Preservative Types

   • Formalin

   Diagnoses:

   • Neoplastic - Carcinoma

   Platform:

   Analyte	Technology Platform
   Protein	Immunohistochemistry

   Pre-analytical Factors:

   Classification	Pre-analytical Factor	Value(s)
   Storage	Storage duration	0 months 4 months 6 months
   Storage	Storage conditions	Unaltered Paraffin-coated
   Storage	Storage temperature	Room temperature (20-25°C) 4°C

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