The influence of treatment sequence in the prognostic value of TMPRSS2‐ERG as biomarker of taxane resistance in castration‐resistant prostate cancer

TMPRSS2-ERG expression in blood has been correlated with low docetaxel benefit in metastatic castration-resistant prostate cancer (mCRPC). This multicenter study aimed to prospectively asses its role as a taxane-resistance biomarker in blood and retrospectively in tumors, exploring also the impact of prior abiraterone/enzalutamide (A/E) in patients and in vitro. TMPRSS2-ERG was tested by quantitative reverse-transcription PCR. We included 204 patients (137 blood and 124 tumor samples) treated with taxanes. TMPRSS2-ERG expression was correlated with prostate-specific antigen (PSA)-progression-free survival (PFS), radiological-PFS (RX-PFS), and overall survival (OS). Independent association with survival was evaluated by multivariate Cox modeling. In vitro ERG knockdown and combinatorial and sequential experiments with enzalutamide and docetaxel were performed in VCaP cells. Prior A/E (HR 1.8, 95% CI 1.2-2.8) and blood TMPRSS2-ERG detection (HR 2, 95% CI 1.1-3.7) were independently associated to lower PSA-PFS. In patients without prior A/E, blood and tumor TMPRSS2-ERG independently predicted lower PSA-PFS (HR 3.3, 95% CI 1.4-7.9 and HR 1.8, 95% CI 1.02-3.3, respectively) to taxanes. When prior A/E was administered, TMPRSS2-ERG was not associated with outcome. There was a significant interaction between blood TMPRSS2-ERG and prior A/E related to PSA-PFS (p = 0.032) and RX-PFS (p = 0.009). In vitro stable ERG inhibition did not sensitize VCaP cells to docetaxel. Concomitant enzalutamide and taxanes were synergistic, but prior enzalutamide reduced docetaxel cytotoxicity in VCaP cells. Enzalutamide induced the expression of neuroendocrine markers and reduced that of E-cadherin. We conclude that prior hormone-therapy may influence taxanes response and TMPRSS2-ERG prognostic value. Thus, multiple and sequential biomarkers are needed in CRPC follow-up evaluation.