Prognostic implications of PSA levels at 7 months in metastatic hormone-sensitive prostate cancer treated with enzalutamide: Landmark analysis of ENZAMET (ANZUP 1304).

5079 Background: ENZAMET (NCT02446405) showed that enzalutamide added to testosterone suppression (TS) with or without docetaxel improves overall survival (OS) compared with TS plus standard non-steroidal anti-androgen (NSAA) in patients with metastatic hormone-sensitive prostate cancer (mHSPC). We assessed PSA levels in ENZAMET participants at 7 months after randomization to determine correlations with OS. In CHAARTED, participants with mHSPC high volume disease (HV), 20% achieved PSA ≤ 0.2 with ADT (androgen deprivation therapy) alone versus 44% with low volume disease (LV) and for HV with ADT + Docetaxel, 36% achieved PSA ≤ 0.2 vs 64% with LV. Methods: Participants were included if they were followed for at least 7 months after randomization, and had availability of PSA and outcome data. Landmark analysis at 7 months used prognostic classifiers as previously identified in SWOG 9346 and CHAARTED of PSA ≤ 0.2 and > 0.2 at 7 months after initiation of therapy. Results: The total number of ENZAMET participants (pts) with PSA at 7 months of ≤0.2ng/mL was 646 of 1125 (57%): 271/562 (48%) in the NSAA arm versus 375/563 (67%) in the ENZA arm. Five-year OS for TS + NSAA (±Doc) arm PSA ≤ 0.2 = 71% vs PSA > 0.2 = 36% and for TS + ENZA (±Doc) arm PSA ≤ 0.2 = 74% vs PSA > 0.2 = 43%. The % of pts with PSA levels at 7 months ≤0.2ng/mL and corresponding 5-year OS outcomes by key prognostic groups (HV vs LV) ± docetaxel is shown (Table). In comparison with CHAARTED in those with HV, 37% achieved PSA ≤ 0.2 with ADT alone versus 61% with LV which increased to 55% for HV and 79% for LV respectively with addition of enzalutamide. In those with HV treated with ADT + D 39% achieved PSA ≤ 0.2 vs 58% with LV increasing to 60% for HV and 74% for LV respectively with addition of enzalutamide. Conclusions: A PSA nadir of ≤0.2 at 7 months is associated with a longer OS regardless of treatment and prognostic group (HV vs LV). Enzalutamide increased the rate of achievement of PSA <0.2 for all groups. Clinical trial information: NCT02446405 . Table: see text