Pain Outcomes in Patients with Metastatic Castration-Resistant Prostate Cancer Treated with (223)Ra: PARABO, a Prospective, Noninterventional Study

(223)Ra, a targeted α-therapy, is approved for the treatment of patients with metastatic castration-resistant prostate cancer (mCRPC) who have bone metastases. In the phase 3 ALSYMPCA study, (223)Ra prolonged survival and improved quality of life versus placebo. Our real-world study, PARABO, investigated pain and bone pain–related quality of life in patients with mCRPC and symptomatic bone metastases receiving (223)Ra in clinical practice. Methods: PARABO was a prospective, observational, noninterventional single-arm study conducted in nuclear medicine centers across Germany (NCT02398526). The primary endpoint was a clinically meaningful pain response (≥2-point improvement from baseline for the worst-pain item score in the Brief Pain Inventory–Short Form). Results: The analysis included 354 patients, who received a median of 6 (223)Ra injections (range, 1–6). Sixty-seven percent (236/354) received 5–6 injections, and 33% (118/354) received 1–4 injections. Of 216 patients with a baseline worst-pain score of more than 1, 59% (128) had a clinically meaningful pain response during treatment. Corresponding rates were 67% (range, 98/146) with 5–6 (223)Ra injections versus 43% (range, 30/70) with 1–4 injections, 60% (range, 60/100) in patients with no more than 20 lesions versus 59% (range, 65/111) in those with more than 20 lesions, and 65% (range, 69/106) in patients without prior or concomitant opioid use versus 54% (range, 59/110) in those with prior or concomitant opioid use. Mean subscale scores (pain severity and pain interference) on the Brief Pain Inventory–Short Form improved during treatment. Conclusion: (223)Ra reduced pain in patients with mCRPC and symptomatic bone metastases, particularly in patients who received 5–6 injections. The extent of metastatic disease did not impact pain response.