Radium-223 in combination with enzalutamide in metastatic castration-resistant prostate cancer: a multi-centre, phase II open-label study.

Radium-223 and enzalutamide are approved agents for patients with metastatic castration-resistant prostate cancer (mCRPC). Combining radium-223 and enzalutamide to improve outcomes is of clinical interest due to their differing modes of action and non-overlapping toxicity profiles.

This phase II study enrolled patients with mCRPC and bone metastases. Patients received six cycles of radium-223 in combination with enzalutamide, followed by enzalutamide alone. The primary endpoint was safety for the combination; secondary endpoints included radiographic/clinical progression-free survival (PFS), PSA PFS, overall survival (OS), change in alkaline phosphatase, patient-reported pain outcomes and skeletal related events.

Forty-five patients received the combination treatment: 42 patients (93.3%) received all six cycles. Fourteen patients (31.1%) developed grade 3 or 4 toxicities, most commonly fatigue and neutropaenia. Fractures during the combination period occurred in four patients (8.9%). A further 13 patients (28.9%) developed fractures after completing combination treatment, giving a total of 17 patients (37.8%) who developed a fracture at any time on study. The median time to fracture was greater than 17.2 months [95% confidence interval (CI), 17.2-not estimable]. The median time to PSA progression was 18.1 months (95% CI, 12.68-22.60) and the median time to radiological/clinical progression was 28.0 months (95% CI, 22.54-not reached). At the primary analysis, 19 (42.2%) out of 45 patients had died with a median OS not reached (mean 34.8 months, standard error 1.4).

In men with progressive mCRPC and bone metastases, the combination of radium-223 and enzalutamide was tolerable with the majority of patients completing the combination treatment. Bone fractures during the combination period were uncommon; however, we did identify a higher incidence of fractures occurring in patients after completing combination treatment. Bone health agents should be administered and bone health should be closely monitored following treatment with radium-223 and enzalutamide.

Therapeutic advances in medical oncology. 2021 Sep 06*** epublish ***

Raymond S McDermott, John Greene, John McCaffrey, Imelda Parker, Sylva Helanova, Anne-Marie Baird, Ausra Teiserskiene, Marvin Lim, Helen Matthews, Olwyn Deignan, John Feeney, Pierre G Thirion, Stephen P Finn, Paul J Kelly

Cancer Trials Ireland, Dublin, Ireland., Cancer Trials Ireland, Innovation House, Glasnevin, Dublin 8, IrelandTallaght University Hospital, Dublin, Ireland Trinity College Dublin, Ireland.