Comparison of ERG oncoprotein expression among matched cohorts of African American and Caucasian American patients with prostate cancer.

Abstract

52 Background: The ERG proto-oncogene is frequently overexpressed in Prostate Cancer (CaP) following genomic fusion, which places ERG under the control of the TMPRSS2 promoter. Recent studies show higher frequency of ERG rearrangement or ERG oncoprotein expression in CaP of Caucasian-American (CA) patients compared to African-American (AA) patients. The frequency of the ERG oncoprotein expression in prostate tumors of matched CA and AA CaP patients is evaluated to better understand the biological basis for differences in prostate cancer between the two populations. Methods: Ninety-one AA CaP patients were matched for age, Gleason sum and pathologic stage to 91 CA CaP patients. All underwent radical prostatectomy between 1993 and 2010. Whole mount prostate specimens were used for immunohistochemical detection of the ERG oncoprotein by an ERG monoclonal antibody (clone 9FY). Individual foci of tumors were noted as either positive or negative. ERG staining data was linked to dinico-pathologic data. Results: Fifty-nine of 91 CA patients (64.8%) and 41191 (45.0%) AA patients had at least one focus of tumor positive for ERG in a whole-mount prostate section (p = 0.0073). The index tumor was positive for ERG expression in 55/89 (61.8%) CA and 24/85 (28.2%) of AA patients (p <0.001). Seventy-seven of 183 (42.1%) individual foci were positive in CA versus 511196 in AA (26.0%; P <0.001). There was a trend towards increased biochemical recurrence in CA patients with ERG positive index tumors. Conclusions: The prevalence of ERG oncoprotein expression is significantly higher among Caucasian- American patients. Differences in pattern of ERG positivity of index and non-index tumors between Caucasian-American and African-American prostate cancer patients and trends towards decreased biochemical recurrence-free survival suggest a more accelerated growth of ERG-positive tumors in Caucasian-American patients. Differences in ERG expression have the potential to delineate biological distinctions of CaP in these patient populations.