Addition of Enzalutamide to Leuprolide and Definitive Radiation Therapy Is Tolerable and Effective in High-Risk Localized or Regional Nonmetastatic Prostate Cancer: Results From a Phase 2 Trial

BACKGROUND: Enzalutamide is an antiandrogen used to treat both metastatic and nonmetastatic prostate cancer. Here we present results from a phase 2 trial designed to determine the safety, tolerability, and efficacy of adding enzalutamide to standard androgen deprivation therapy with radiation therapy in high-risk localized or regional, nonmetastatic patients with prostate cancer. METHODS AND MATERIALS: Enrollment criteria included at least 2 of the following: stage cT3a/b, prostate specific antigen (PSA) ≥20 ng/mL, Gleason grade 8 to 10, ≥33% core involvement on biopsy, or pelvic lymph node involvement on computed tomography or magnetic resonance imaging. Patients with metastatic disease were excluded. All patients received 24 months of leuprolide and enzalutamide, and 5 weeks of intensity modulated radiation therapy followed by a brachytherapy boost. Adverse events (AE), PSA, testosterone, and basic laboratory tests were then followed for up to 36 months. Primary outcomes were safety and tolerability and PSA complete response rate (PSA-CR, defined as PSA ≤0.3). Secondary outcomes included time to biochemical recurrence (BCR; nadir + 2 ng/mL). RESULTS: Sixteen patients were enrolled; 2 were ineligible and 3 withdrew before starting treatment. Median age at enrollment was 69.0 years (interquartile range [IQR] 11.5). Median treatment duration was 24.0 months (IQR 11.9). Median follow-up time was 35.5 months (IQR 11.2), and 9 of 11 (81.8%) patients completed the 36 months of follow-up. One of 11 (9%) patients had grade 4 AE (seizure), and no grade 5 AE were reported. Four of 11 (36.4%) patients had grade 3 AE, such as erectile dysfunction and hot flashes. All patients achieved PSA-CR, and median time to PSA-CR was 4.2 months (IQR 1.4). At 24 months follow-up, 0 of 11 (0%) patients had a biochemical recurrence. At 36 months, 1 of 9 (11.1%) patient had a biochemical recurrence. Of note, this patient did not complete the full 24 months of enzalutamide and leuprolide due to AEs. CONCLUSIONS: Enzalutamide in combination with standard androgen deprivation therapy and radiation therapy was well-tolerated and effective warranting further study in a randomized controlled trial.