The Benefit of Combining Docetaxel with Androgen Deprivation Therapy in Localized and Metastatic Hormone-sensitive Prostate Cancer is Predicted by ERG Expression: An Analysis of Two GETUG Phase 3 Trials

BACKGROUND AND OBJECTIVE: Docetaxel has become a standard component of care for advanced prostate cancer (PC); however, its benefits are not universal among patients. A subset of PC cases exhibit TMPRSS2-ERG gene fusion, resulting in ERG overexpression in tumors. Our aim was to assess biomarkers for docetaxel efficacy in men with hormone-sensitive PC (HSPC). METHODS: Pretreatment prostate biopsies were obtained from participants in two randomized phase 3 clinical trials investigating docetaxel in high-risk localized PC (GETUG 12) and metastatic HSPC (GETUG 15). Immunohistochemistry staining for Ki67, PTEN, RB, and phosphorylated RB was conducted for GETUG 12 samples, and ERG staining for GETUG 12 and GETUG 15 samples. We examined biomarker association with outcomes using univariate and multivariable analyses adjusted for other validated prognostic factors. KEY FINDINGS AND LIMITATIONS: Among GETUG 12 patients, Ki67 was associated with a worse relapse-free survival (RFS; hazard ratio [HR] 1.72; p = 0.0092). A pooled analysis for the two trials (pinteraction = 0.056) revealed that docetaxel-based chemotherapy improved failure-free survival for patients with ERG-positive cancer (HR 0.58; p = 0.03), but not patients with ERG-negative cancer (HR 1.08; p = 0.72). In the ERG-positive subgroup in GETUG 12 (high-risk localized PC), median RFS was 7.79 yr with androgen deprivation therapy (ADT) alone, and was not reached with ADT + docetaxel. In the ERG-negative subgroup, median progression-free survival (mPFS) was 7.79 yr with ADT alone versus 7.08 yr with ADT + docetaxel. In the ERG-positive subgroup in GETUG 15 (metastatic HSPC), mPFS was 10.7 mo with ADT alone versus 18.8 mo with ADT + docetaxel. In the ERG-negative subgroup, mPFS was 10.6 mo with ADT alone versus 13.2 mo with ADT + docetaxel. CONCLUSIONS AND CLINICAL IMPLICATIONS: Ki67 may serve as a prognostic factor in HSPC, while ERG expression appears to predict a response to docetaxel in both high-risk localized and metastatic HSPC. PATIENT SUMMARY: We assessed factors that could predict outcomes after docetaxel chemotherapy in patients with advanced prostate cancer. We found that expression of a protein called ERG can predict a good response to docetaxel in these patients.