Introduction: Radium-223 is an approved survival-prolonging treatment option in men with castration-resistant prostate cancer (mCRPC) and bone metastases. In the registration trial (ALSYMPCA), no regular imaging was mandated. We aimed to analyze men with metastatic mCRPC treated with radium-223 who had bone scintigraphy for staging and treatment monitoring.
Patients and methods: Retrospective chart review was performed of mCRPC patients who received 6 cycles of radium-223 and who underwent bone scintigraphy before start of radium-223 and after 3 and 6 cycles of treatment.
Results: Nineteen patients with a median age of 74 years met the selection criteria and were included in the analysis. On bone scintigraphy, 4 of 19 patients showed a total of ≥ 2 new lesions after 3 cycles of radium-223 therapy, but 3 of 4 patients did not have ≥ 2 new lesions after 6 cycles, meeting the criteria for bone scintigraphy flare. Of these 4 patients, 2 received radium-223 before docetaxel therapy, and all 4 had concomitant treatment with denosumab. In the entire cohort, 3 of 19 patients showed soft tissue progression on computed tomography after 3 cycles of radium-223.
Conclusion: Bone scintigraphy flare in patients undergoing therapy with radium-223 was observed. Bone scintigraphy data acquired during treatment with radium-223 should be interpreted with caution, and treatment should not be changed according to increase in number of lesions on bone scintigraphy alone after 3 cycles of radium-223.
Keywords: Bone metastases; Flare phenomenon; Radium-223; Targeted alpha therapy; Treatment monitoring.
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