Preliminary results from a phase II trial of docetaxel before castration with degarelix in men with newly diagnosed metastatic prostate cancer.

Abstract

116 Background: Randomized trials have demonstrated a survival advantage to administering docetaxel (D) shortly after initiation of androgen deprivation therapy (ADT) in men with newly diagnosed hormone sensitive metastatic prostate cancer (hsMPC). Clinical trials in breast cancer, research in prostate cancer cell lines, and pharmacokinetic analyses of D clearance in the castrate state, suggest increased efficacy of chemotherapy administered separately from hormone suppression. We proposed that treatment with D before ADT might improve outcomes in newly diagnosed hsMPC. Methods: In an ongoing phase II study (NCT03069937), men with newly diagnosed hsMPC were treated with 4 cycles of D (75mg/m2) every 21 days without ADT followed by 2 cycles of D concurrent with the LHRH antagonist degarelix (Deg) administered every 4 weeks. The Deg alone was continued for a total of 7 injections. Men were trial eligible with high or low volume disease by CHAARTED criteria. Bicalutamide was allowed for < 30 days before trial entry, but LHRH directed therapy was not permitted. The primary endpoint for this trial is percentage of men obtaining PSA < 0.2 ng/ml. Pre-specified secondary endpoints examined here after 4 cycles of docetaxel alone are safety, and efficacy defined by PSA (decrease by > 50%) and radiographic responses. Results: At time of this abstract, 50 patients have been enrolled to trial. Two patients withdrew after 1 cycle of D, and 4 patients have not yet completed 4 cycles. Of the 50 patients evaluable for safety, 6 (12%) had Grade 3 toxicities related to D. No Grade 4/5 toxicities were reported. Of patients who completed 4 cycles of D, 24/44 (55%) had a PSA response and 34/44 (77%) had PSA decline from baseline. All but two patients with declining PSA had stable or improved radiographic imaging. Six of the 44 patients (14%) had PSA progression (>25% increase) with D therapy, 3 of whom also had radiographic progression. Every patient with PSA response after 4 cycles D had PSA decline after 2 cycles. No patient with PSA decline after 2 cycles had PSA progression after 4 cycles. PSA response rate was stratified by baseline variables in table below. Conclusions: In hsMPC patients, 4 cycles D without ADT appears to be a safe and active therapy. Treatment with bicalutamide prior to the start of D predicts poorer PSA response. This result strengthens our hypothesis that sensitivity of hsMPC to taxane therapy may be enhanced if ADT is postponed. Baseline genomics will be analyzed, and we hope to correlate responses to D alone with later primary efficacy outcomes. Clinical trial information: NCT03069937. [Table: see text]