Whole-body diffusion-weighted magnetic resonance imaging to assess bone response in patients with hormone-sensitive metastatic prostate cancer randomly assigned to receive androgen deprivation + enzalutamide ± zoledronic acid.

46 Background: Bone is frequently involved in metastatic hormone sensitive prostate cancer (mHSPC). Whole-body diffusion-weighted magnetic resonance imaging (WB-DW-MRI) is a promising imaging technique for the assessment of bone response in prostate cancer. It is not known whether the addition of antiresorptive agents can improve disease response in bone in mHSPC patients undergoing next generation hormonal agents. Methods: In this multicenter phase II study patients with de novo or relapsed mHSPC and bone metastases at bone scan were randomly allocated with a 1:1 ratio to receive either androgen deprivation therapy (ADT) plus Enzalutamide (E arm) or the same combination with the addition of Zoledronic Acid (EZ arm). The study was designed to observe a significant increase in bone response rate in the experimental arm after 12 months of treatment, as assessed through WB-DW-MRI. WB-DW-MRI was performed centrally at baseline and after 6 and 12 months and images were evaluated by the same radiologist. Results: From February 2018 to June 2021, 126 mHSPC patients were randomized, 64 in EZ arm and 62 in E arm. A total of 111 patients, 54 from E arm and 57 from EZ arm, were eligible for WB-DW-MRI assessment (15 patients were excluded because of the absence of bone target lesions at MRI or specific contraindications to MRI). Bone response at 6 months was observed in 41 patients (76%) in E arm and 41 patients (72%) in EZ arm; the corresponding bone response at 12 months were 44 (82%) and 44 (77%), respectively (OR 0.77; 95%IC 0.30-1.93; p = 0.6). Complete response was the best overall bone response after 12 months in 9 patients (17%) from E arm and in 11 patients (19%) from EZ arm. In the same period, treatment was interrupted due to disease progression in 7 (13%) and 7 (12%) patients in E and EZ arm, respectively. Conclusions: The addition of Zoledronic Acid to Enzalutamide and ADT did not improve bone disease response in patients with mHSPC. WB-DW-MRI was able to detect bone responses in a great proportion of patients. Clinical trial information: NCT03336983 .