Analytic validation of a clinical-grade PTEN immunohistochemistry assay in prostate cancer by comparison with PTEN FISH

• Published in: Modern pathology Vol. 29; no. 8; pp. 904 - 914
• Main Authors: Lotan, Tamara L, Wei, Wei, Ludkovski, Olga, Morais, Carlos L, Guedes, Liana B, Jamaspishvili, Tamara, Lopez, Karen, Hawley, Sarah T, Feng, Ziding, Fazli, Ladan, Hurtado-Coll, Antonio, McKenney, Jesse K, Simko, Jeffrey, Carroll, Peter R, Gleave, Martin, Lin, Daniel W, Nelson, Peter S, Thompson, Ian M, True, Lawrence D, Brooks, James D, Lance, Raymond, Troyer, Dean, Squire, Jeremy A
• Format: Journal Article
• Language: English
• Published: New York Elsevier Inc 01.08.2016; Nature Publishing Group US; Elsevier Limited
• Subjects: 631/67/589/466; 82/51; Automation; Biomarkers; Biomarkers, Tumor - analysis; Biomarkers, Tumor - genetics; British Columbia; Cancer research; Epigenetics; Gene Deletion; Gene Dosage; Genetic Predisposition to Disease; Heterozygote; Homozygote; Humans; Immunohistochemistry; In Situ Hybridization, Fluorescence; Laboratory Medicine; Male; Medical research; Medical schools; Medicine; Medicine & Public Health; MicroRNAs; Mutation; original-article; Pathology; Phenotype; Predictive Value of Tests; Prostate cancer; Prostatic Neoplasms - enzymology; Prostatic Neoplasms - genetics; Prostatic Neoplasms - pathology; Prostatic Neoplasms - surgery; Proteins; PTEN Phosphohydrolase - analysis; PTEN Phosphohydrolase - genetics; Reproducibility of Results; Retrospective Studies; Tissue Array Analysis; Tumors; United States; United States; British Columbia; Canada; San Francisco California; United States > US; Virginia; Baltimore Maryland
• ISSN: 0893-3952; 1530-0285
• DOI: 10.1038/modpathol.2016.88

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.