[798] Novel Dual Color Immunohistochemical Method for Detecting ERG and PTEN Status in Prostate Carcinoma

Ritu Bhalla, Lakshmi P Kunju, Scott A Tomlins, Kelly Christopherson, Connie Cortez, Juan M Mosquera, Gary Pestano, Arul Chinnaiyan, Nallasivam Palanisamy. University of Michigan, Ann Arbor, MI; Ventana Medical System, Tucson, AZ; Weill Cornell Medical College, New York, NY; Michigan Center for Translational Pathology, Ann Arbor, MI; Howard Hughes Medical Institute, Ann Arbor, MI

Background: TMPRSS2-ERG gene fusions occur in 50% of prostate cancers (PCA) and result in the overexpression of a chimeric fusion transcript that encodes a truncated ERG product, which can be detected by immunohistochemistry (IHC). PTEN is a key tumor suppressor gene, implicated in many cancers, including PCA. Loss of PTEN, detected by fluorescent in situ hybridization (FISH) has been associated with poor prognosis. Concurrent PTEN deletion (del) and TMPRSS2-ERG fusions have been reported to be associated with an unfavorable outcome. We developed a novel automated dual color ERG and PTEN IHC assay to evaluate ERG and PTEN status as a single procedure.
Design: A dual immunostain, utilizing rabbit antibodies against ERG and PTEN, was performed on PCA tissue micro-arrays using automated protocols on the Discovery XT system (Ventana). A total of 120 cases from 101 localized (loc) and 19 metastatic (met) PCA were evaluated. Nuclear ERG expression was scored as present or absent (endothelial staining was used as positive control). Cytoplasmic PTEN staining was scored as normal (increased or equal staining compared to adjacent benign acini), and negative (decreased or absent staining). IHC results were compared with FISH results for PTEN del status.
Results: Out of 120 cases evaluated, 55 (46%) ERG positive (50 loc and 5 met PCA) and 33 (28%) PTEN deleted cases (20 loc and 13 met) were identified by IHC. Of the 55 ERG positive cases, PTEN loss was observed in 17(31%) cases (12 loc and 5 met) by IHC. PTEN status was concordant in 101 cases (84% sensitivity) by both IHC and FISH. Among 33 PTEN deleted cases as identified by IHC, 27 were confirmed (81% specificity) by FISH. IHC could not distinguish heterozygous and homozygous deletion status of PTEN.
Conclusions: Automated dual ERG-PTEN IHC is simple, reliable and easy to perform for the simultaneous assessment of ERG and PTEN protein expression in PCA. Antibody based detection of PTEN shows a high concordance with FISH, which may be an alternative for evaluation of PTEN status in PCA. We confirm the previously described association between PTEN loss and ERG fusion in our cohort. This assay may potentially be useful for screening patients to select them for therapeutic targeting of these pathways in high risk PCA.
Category: Genitourinary (including renal tumors)

Monday, March 19, 2012 1:00 PM

Poster Session II # 161, Monday Afternoon

 

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