EMBARK: Testosterone recovery to >250 ng/dL following treatment suspension.

5088 Background: The phase 3 EMBARK trial demonstrated significantly longer metastasis-free survival and overall survival for enzalutamide plus leuprolide (enzalutamide combination) vs leuprolide alone in patients with prostate cancer and high-risk biochemical recurrence (hrBCR). In EMBARK, patients with prostate-specific antigen (PSA) 250 ng/dL during treatment suspension in patients treated with enzalutamide combination. Methods: Eligible patients had hrBCR, with a PSA doubling time of ≤9 months. Patients were randomized 1:1:1 to enzalutamide + leuprolide, leuprolide alone, or enzalutamide monotherapy. Patients who suspended treatment at week 37 reinitiated treatment upon PSA increase to protocol-defined levels. Testosterone levels were assessed every 12 weeks. Results: In the enzalutamide combination group, 320 patients suspended treatment. During treatment suspension, testosterone recovery to > 250 ng/dL occurred in 108 patients (33.8%) (Table). Among those who recovered their testosterone, median and mean time to recovery was 5.6 months and 6.8 months, respectively, although some patients had delayed recovery (Table). Conclusions: Testosterone recovery to > 250 ng/dL during treatment suspension was observed in approximately one-third of patients treated with enzalutamide combination. While average time to testosterone recovery among those who recovered was ~6 months, recovery was delayed in some patients. Disclosure: Pfizer’s generative AI tool MAIA was used in developing this abstract; the authors reviewed, edited, and take full responsibility for the content. Clinical trial information: NCT02319837 . Enza combination(N=320) Patients who reached testosterone recovery, n (%) 108 (33.8) Time to testosterone recovery >250 ng/dL, months † Median (range) 5.6 (0.0–22.1) Mean (SD) 6.8 (2.87) The data cutoff date was January 31, 2023. † Time to testosterone recovery during treatment suspension is based on the number of patients who reached testosterone recovery, and was defined as the time from the date of the start of treatment suspension to the date of the first occurrence of testosterone >250 ng/dL. The summary is based on testosterone records during treatment suspension from patients who had treatment suspension and non-missing testosterone records after treatment suspension. For patients who reinitiated treatment, testosterone records after reinitiation were not considered.