Analytic Validation of a Clinical-Grade PTEN Immunohistochemistry Assay in Prostate Cancer by Comparison With PTEN FISH

Mod Pathol. 2016 Aug;29(8):904-14. doi: 10.1038/modpathol.2016.88. Epub 2016 May 13.

Abstract

PTEN loss is a promising prognostic and predictive biomarker in prostate cancer. Because it occurs most commonly via PTEN gene deletion, we developed a clinical-grade, automated, and inexpensive immunohistochemical assay to detect PTEN loss. We studied the sensitivity and specificity of PTEN immunohistochemistry relative to four-color fluorescence in situ hybridization (FISH) for detection of PTEN gene deletion in a multi-institutional cohort of 731 primary prostate tumors. Intact PTEN immunostaining was 91% specific for the absence of PTEN gene deletion (549/602 tumors with two copies of the PTEN gene by FISH showed intact expression of PTEN by immunohistochemistry) and 97% sensitive for the presence of homozygous PTEN gene deletion (absent PTEN protein expression by immunohistochemistry in 65/67 tumors with homozygous deletion). PTEN immunohistochemistry was 65% sensitive for the presence of hemizygous PTEN gene deletion, with protein loss in 40/62 hemizygous tumors. We reviewed the 53 cases where immunohistochemistry showed PTEN protein loss and FISH showed two intact copies of the PTEN gene. On re-review, there was ambiguous immunohistochemistry loss in 6% (3/53) and failure to analyze the same tumor area by both methods in 34% (18/53). Of the remaining discordant cases, 41% (13/32) revealed hemizygous (n=8) or homozygous (n=5) PTEN gene deletion that was focal in most cases (11/13). The remaining 19 cases had two copies of the PTEN gene detected by FISH, representing truly discordant cases. Our automated PTEN immunohistochemistry assay is a sensitive method for detection of homozygous PTEN gene deletions. Immunohistochemistry screening is particularly useful to identify cases with heterogeneous PTEN gene deletion in a subset of tumor glands. Mutations, small insertions, or deletions and/or epigenetic or microRNA-mediated mechanisms may lead to PTEN protein loss in tumors with normal or hemizygous PTEN gene copy number.

Publication types

  • Comparative Study
  • Multicenter Study
  • Validation Study

MeSH terms

  • Biomarkers, Tumor / analysis*
  • Biomarkers, Tumor / genetics*
  • British Columbia
  • Gene Deletion
  • Gene Dosage
  • Genetic Predisposition to Disease
  • Heterozygote
  • Homozygote
  • Humans
  • Immunohistochemistry*
  • In Situ Hybridization, Fluorescence*
  • Male
  • PTEN Phosphohydrolase / analysis*
  • PTEN Phosphohydrolase / genetics*
  • Phenotype
  • Predictive Value of Tests
  • Prostatic Neoplasms / enzymology*
  • Prostatic Neoplasms / genetics*
  • Prostatic Neoplasms / pathology
  • Prostatic Neoplasms / surgery
  • Reproducibility of Results
  • Retrospective Studies
  • Tissue Array Analysis
  • United States

Substances

  • Biomarkers, Tumor
  • PTEN Phosphohydrolase
  • PTEN protein, human