A Phase Ii Multicenter Biomarker Trial To Study The Predictive Value Of Tmprss2-Erg Before Enzalutamide Treatment In Chemo-Naive Metastatic Castration-Resistant Prostate Cancer.

5040 Background: TMPRSS2-ERG fusion gene is a common driver of prostate cancer. The PREMIERE study is a phase II, single arm open-label, multicentre, clinical trial designed to analyse the predictive/prognostic value of TMPRSS2-ERG in first-line chemo-naïve mCRPC patients treated with enzalutamide. Methods: We centrally evaluated TMPRSS2-ERG in diagnostic samples using PCR, FISH and IHC for ERG. Among exploratory biomarkers we included plasma DNA, AR copy number by ddPCR and CTC by AdnaTest. PCWG2 criteria were used for outcome evaluation. We correlated TMPRSS2-ERGand other exploratory biomarkers with mCRPC outcomes. Results: Ninety eight patients with median age 77 y (range 59-95), ECOG 0/1 (54/46%) with mts located in bone (82%), LN (48%) and visceral (17%). With a median FU of 37.3 months, PSA response was PSA50: 82% and PSA90: 53%; median PSA-PFS was 13.7m (95%CI 10.2-19.0), Rad-PFS 26.7m (95%CI: 22.0-NA) and OS 37.5m (95%IC: 33.7-NA). TMPRSS2-ERG was detected in 32 pts (33%), AR gain in 11 pts and CTCs in 35 pts. No differences were observed based on TMPRSS2-ERG status for PSA response (PSA50: 81% vs 83%; p=0.8), PSA-PFS (median 12.8 vs 14.7m; HR 0.98; 95%CI 0.58-1.67; p=0.95), Rad-PFS (median 28.4 vs 26.4m; HR 1.02; 95% 0.53-1.96, p=0.95) or OS (median 36.9 vs 38.1m; HR 1.23; 95%CI 0.69-2.21, p=0.48). Plasma AR gain was associated with worse PSA-PFS (median 4.2 vs 14.7 m; p<0.0001), Rad-PFS (median 3.6 vs 28.4m; p<0.0001) and OS (median 12.7 vs 38.1m; p<0.0001). Plasma DNA and CTCs were also associated with worse outcome. Multivariate analyses of exploratory biomarkers are included in the table. Conclusions: The fusion gene TMPRSS2-ERG is not predictive nor prognostic on enzalutamide treatment in first-line chemo-naïve mCRPC patients. Plasma AR gain and CTCs are strong independent biomarkers associated with adverse outcome. Multivariate analysis of exploratory biomarkers. Clinical trial information: NCT02288936. [Table: see text]