To Örebro University

Prostate cancer is a clinically heterogeneous and multifocal disease. More than 80% of patients with prostate cancer harbor multiple geographically discrete cancer foci at the time of diagnosis. Emerging data suggest that these foci are molecularly distinct consistent with the hypothesis that they arise as independent clones. One of the strongest arguments is the heterogeneity observed in the status of E26 transformation specific (ETS) rearrangements between discrete tumor foci. The clonal evolution of individual prostate cancer foci based on recent studies demonstrates intertumoral heterogeneity with intratumoral homogeneity. The issue of multifocality and interfocal heterogeneity is important and has not been fully elucidated due to lack of the systematic evaluation of ETS rearrangements in multiple tumor sites. The current study investigates the frequency of multiple gene rearrangements within the same focus and between different cancer foci. Fluorescence in situ hybridization (FISH) assays were designed to detect the four most common recurrent ETS gene rearrangements. In a cohort of 88 men with localized prostate cancer, we found ERG, ETV1, and ETV5 rearrangements in 51% (44/86), 6% (5/85), and 1% (1/86), respectively. None of the cases demonstrated ETV4 rearrangements. Mutual exclusiveness of ETS rearrangements was observed in the majority of cases; however, in six cases, we discovered multiple ETS or 50 fusion partner rearrangements within the same tumor focus. In conclusion, we provide further evidence for prostate cancer tumor heterogeneity with the identification of multiple concurrent gene rearrangements. Laboratory Investigation (2011) 91, 404-412; doi: 10.1038/labinvest.2010.179; published online 25 October 2010

OBJECTIVES To interrogate multifocal prostate cancer (PCa) to determine its predilection for metastasis, using ERG rearrangement as marker of clonality. A hallmark of PCa is that distinct tumor foci may arise independently, which has important biological and clinical implications. Recent studies characterizing ERG-rearranged PCa possessing intrafocal homogeneity but interfocal heterogeneity support this hypothesis. METHODS We studied 26 patients who underwent prostatectomy and lymphadenectomy with at least 2 distinct PCa foci and 1 lymph node (LN) metastasis. Each focus was assessed for size, Gleason score, ERG rearrangement, and TMPRSS2-ERG transcript. RESULTS Fifteen of 26 cases exhibited interfocal homogeneity with regard to ERG rearrangement (ie, presence vs absence of ERG rearrangement). ERG rearrangement was present in all foci for 6 and absent in all foci for 9 cases. Two cases revealed interfocal heterogeneity with regard to rearrangement mechanism ( ie, rearrangement through insertion or deletion). Eight of 26 cases revealed interfocal heterogeneity with regard to rearrangement status. In all cases with at least 1 ERG rearranged focus, we found the corresponding LN metastasis harboring an ERG rearrangement. Interestingly, in a subset of cases the rearrangement status in the LN did not correspond to size or Gleason score. All but 2 ERG rearranged foci had detectable TMPRSS2-ERG transcript levels. CONCLUSIONS When multifocal PCa demonstrates both ERG-positive and ERG-negative foci, the positive foci have a greater predilection for metastasis. Larger studies are needed to confirm the potential additional risk an ERG rearranged focus confers on the likelihood of disease progression. UROLOGY 75: 762-767, 2010. (C) 2010 Elsevier Inc.

Overtreatment is a major concern in prostate cancer (PCa) management, as no adequate prognostic tool exists to separate indolent from aggressive disease at time of diagnosis. Androgen deprivation therapy (ADT) is the standard treatment of locally recurrent or metastatic PCa and although most men respond well to ADT initially, inevitably a resistance to the treatment develops. Men with tumor growth despite the androgen-depleted environment are considered to have castration resistant PCa (CRPC). After developing CRPC, the median survival time is typically less than two years. Since the initial discovery of ERG rearrangement in PCa, several studies have investigated the association between ERG rearrangement and clinical outcome of PCa with discrepant results. Few studies have examined the association between ERG rearrangement and CRPC, despite the fact that the most common fusion partners to ERG are androgen regulated. In this study we investigated the association between ERG status and time to CRPC.

We assessed the ERG status in a cohort of 220 men initially managed by watchful waiting and treated with ADT at disease progression. There was no statistically significant association between ERG status and time from start of ADT to CPRC, or start of ADT to PCa-specific death. However, men harboring the ERG rearrangement did have a significantly shorter time between time of diagnosis and start of hormonal treatment, compared to men without the rearrangement (HR: 1.81; 95% CI: 1.23- 2.65), suggesting that ERG rearrangement is indicative of a more aggressive subtype of PCa./p>

The ERG rearrangement is identified in approximately 50% of prostate cancer (PCa) screened cohorts and is known to be highly specific. This genetic aberration, most commonly leading to the TMPRSS2-ERG fusion, but also SLC45A3-ERG or NDRG1- ERG fusions, all leading to an over expression of a truncated ERG protein. Most studies have applied in situ hybridization (FISH) methods or mRNA based assays to investigate the ERG status. Recently, studies showed that ERG protein levels assessed by ERG antibodies can be used as a surrogate marker for ERG rearrangement. In the current study we investigate ERG status on a series of diagnostic biopsies using DNA-, mRNA- and protein based assays. We formally compare three assay results (i.e. FISH, fusion mRNA and immunohistochemistry) to identify which method could be most appropriate to use when having limited amount of tissue. ERG rearrangement was found in 56% of the cases. Comparing ERG rearrangement status by FISH with ERG over expression and TMPRSS2-ERG fusion transcript we found 95.1% (154/162, Fisher’s exact test 9.50E-36) and 85.2% (138/162, Fisher’s exact test 7.26E-22) concordance, respectively. We show that the ERG antibody highly correlates with the ERG rearrangement with high sensitivity and specificity. We also identified the most common TMPRSS2-ERG isoform in the majority of ERG rearranged cases. These results provide compelling evidence that the ERG antibody can be used to further investigate the role of ERG in PCa.