Xofigo (radium-223 dichloride) is an alpha-emitting pharmaceutical, which was approved for the treatment of patients with castration-resistant prostate cancer (CRPC), symptomatic bone metastases, and no known visceral metastatic disease. The long-term safety profile of Xofigo is evaluated in the prospective REASSURE study, which estimates the incidence rates of second primary malignancies in patients with CRPC receiving Xofigo.