ERG protein expression and genomic rearrangement status in primary and metastatic prostate cancer—a comparative study of two monoclonal antibodies

Abstract

BACKGROUND: Overexpression of the ERG protein is highly prevalent in prostate cancer (PCa) and commonly results from gene fusions involving the ERG gene. Recently, N-terminal epitope-targeted mouse and a C-terminal epitope-targeted rabbit monoclonal anti-ERG antibody (ERG-MAbs) have been introduced for the detection of the ERG protein. Independent studies reported that immunohistochemistry (IHC) with both ERG-MAbs highly correlates with the underlying ERG gene rearrangement status. However, comparative studies of both antibodies are lacking. Here, we are among the first to compare the mouse ERGMAb with the rabbit ERG-MAb for their concordance on the same PCa cohort. Furthermore, we assessed whether the ERG protein expression is conserved in lymph node and distant PCa metastases. METHODS: We evaluated tissue microarrays of 278 specimens containing 265 localized PCa, 29 lymph node, 30 distant metastases and 13 normal prostatic tissues. We correlated ERG protein expression with ERG rearrangement status using an ERG break-apart fluorescence in-situ hybridization assay and IHC of both ERG-MAbs. RESULTS: ERG expression and ERG rearrangement status were highly concordant regardless of whether the mouse or rabbit ERG-MAb was used (97.8% versus 98.6%, respectively). Of interest, both ERG antibodies reliably detected the ERG expression in lymph node and distant PCa metastases, of which a subset underwent decalcification. Lymphocytes only revealed immunoreactivity using the rabbit ERG-MAb. If ERG protein expression was present in localized PCa, we observed the same pattern in the corresponding lymph node metastases. CONCLUSIONS: By demonstrating a broad applicability of IHC to study ERG protein expression using either antibody, this study adds an important step toward a facilitated routine clinical application. Further, we demonstrate that the clonal nature of the ERG rearrangement is not restricted to the genomic level, but proceeds in the proteome. Together, our results simplify future efforts to further eliucidate the biological role of ERG in PCa.

Comparison of different prostatic markers in lymph node and distant metastases of prostate cancer

“…Since TMPRSS2-ERG fusion highly correlates with ERG overexpression, the newly available monoclonal antibodies displaying ERG overexpression open up the opportunity for routine utilization. 11,32 ERG immunoreactivity was present in half of the primary prostate cancers being consistent with the frequency of TMPRSS2-ERG fusion and the findings of other immunohistochemical studies. 11,33,34 We found an expression of ERG in approximately half of the lymph node metastases similar to the study of Hoogland et al 33 with six out of nine lymph nodes expressing ERG.…”

“…11,32 ERG immunoreactivity was present in half of the primary prostate cancers being consistent with the frequency of TMPRSS2-ERG fusion and the findings of other immunohistochemical studies. 11,33,34 We found an expression of ERG in approximately half of the lymph node metastases similar to the study of Hoogland et al 33 with six out of nine lymph nodes expressing ERG. In distant metastases, fluorescence in situ hybridization analyses have shown an occurrence of TMPRSS2-ERG rearrangements in 25-35%.…”

“…11 In brief, slides were incubated with the primary antibody (DAKO, Hamburg, Germany and BioLogo, Kronshagen, Germany) ( Table 1) for 30 min at room temperature. Antibody dilution was performed using a Ventana diluent.…”

“…7,8 In contrast to PSA, prostate-specific membrane antigen (PSMA) and prostein (also known as p501s or SLC45A3) were recently described to be highly specific for prostatic tissue. 9,10 Since TMPRSS2-ERG rearrangements, leading to an ETSrelated gene (ERG) overexpression, 11 are amongst the most common and disease-specific genetic alterations in locally defined prostate cancer, [12][13][14] ERG might be of diagnostic potential. While TMPRSS2-ERG is an early event in prostate cancer, 11,15 androgen receptor (AR) amplifications leading to an AR overexpression are linked to advanced prostate cancer stages as well as hormone-refractory metastases.…”

“…9,10 Since TMPRSS2-ERG rearrangements, leading to an ETSrelated gene (ERG) overexpression, 11 are amongst the most common and disease-specific genetic alterations in locally defined prostate cancer, [12][13][14] ERG might be of diagnostic potential. While TMPRSS2-ERG is an early event in prostate cancer, 11,15 androgen receptor (AR) amplifications leading to an AR overexpression are linked to advanced prostate cancer stages as well as hormone-refractory metastases. 16,17 While these above-mentioned markers are mainly investigated in primary prostate cancer, studies including metastatic prostate cancer are rare or absent.…”