Abstract A049: Immunohistochemical detection of ERG, ETV1, ETV4, and PTEN in prostate tumor specimens reveals the heterogeneity of multi-focal prostate cancer
Authors: Tan Shyh-Han , Schafer Cara , Young Denise , Jiang Jiji , Song Yingjie , Dobi Albert , Petrovics Gyorgy , Drake Bettina F. , Chesnut Gregory T. , Sesterhenn Isabell A. 
Published: June 2023

Abstract
Introduction: ETS gene rearrangements involving ERG, ETV1 and ETV4, as well as PTEN deletions are among the most common genomic alterations in prostate cancer. Although these events are found to be mutually exclusive, the multifocality of prostate cancer suggests that they may co-occur in some tumors. The immunohistochemistry (IHC) detection of both ERG overexpression and PTEN protein loss are reliable substitutes for fluorescence in situ hybridization (FISH) assay to probe genomic alterations. The lack of specific antibodies that can discriminate between multiple ETS factors, however, has limited the evaluation for the co-occurrence of these genomic alterations in prostate cancer. Improving our ability to identify the multifocality or inter-focal heterogeneity of tumors can enhance our understanding of biological mechanisms of tumor initiation and progression, and help stratify patients for treatment. Methods: Using monoclonal antibodies (mAbs) that we developed against ETV1 and ETV4, we examined their expression in relation to ERG and PTEN expression by IHC using two TMAs constructed from primary prostate cancer specimens of independent patient cohorts: one was constructed from multiple 1 mm cores representing distinct tumor focus from multifocal tumors from 50 African American (AA) and 50 Caucasian American (CA) men; the other, from a single 2 mm core of individual tumors from a cohort of 152 AA and 304 CA men. Positive expression for each ETS factor and PTEN were evaluated for association with race and clinico-pathologic features that include PSA at diagnosis, Gleason score, pathologic T stage, biochemical recurrence, and metastasis. Univariate analysis of BCR free survival as a function of ERG, ETV1 and ETV4 and PTEN expression was performed for both patient cohorts. Results: ERG(+) expression alone or in combination with PTEN loss were significantly higher in CA men in both patient cohorts. When expression of ETS factors were evaluated together with PTEN status, positive expression of ETS factors and PTEN loss were significantly more prevalent among CA men in both patient cohorts ETV1 and ETV4 expression were detected at 5% or less in both patient cohorts. Cases harboring tumor foci that were positive for more than one marker evaluated frequently showed either intra-tumor or inter-tumor heterogeneity. Univariate analysis of PTEN-ETS protein expression status and BCR free survival showed that patients with loss of PTEN expression trends towards poorer BCR free survival regardless of ETS expression status. Conclusion: We showed that the IHC detection of multiple aberrantly expressed proteins such as ERG, ETV1, ETV4 and PTEN in prostate tumor specimens using highly specific mAbs can reveal the heterogeneity and multi-focality in prostate cancer, which could be used to enhance the stratification of patients for novel treatment strategies.
Citation Format: Shyh-Han Tan, Cara Schafer, Denise Young, Jiji Jiang, Yingjie Song, Albert Dobi, Gyorgy Petrovics, Bettina F. Drake, Gregory T. Chesnut, Isabell A. Sesterhenn. Immunohistochemical detection of ERG, ETV1, ETV4, and PTEN in prostate tumor specimens reveals the heterogeneity of multi-focal prostate cancer [abstract]. In: Proceedings of the AACR Special Conference: Advances in Prostate Cancer Research; 2023 Mar 15-18; Denver, Colorado. Philadelphia (PA): AACR; Cancer Res 2023;83(11 Suppl):Abstract nr A049.