Pain response in a population-based study of radium-223 (Ra223) for metastatic castration-resistant prostate cancer.

Introduction: Clinical trials have shown that radium-223 (Ra223) can prolong survival and improve quality of life in patients with metastatic castration-resistant prostate cancer (mCRPC). The objectives of this study were to evaluate pain responses with Ra223 at a population-based level and to determine if there is an association between pain response and alkaline phosphatase (ALP) response.

Methods: All patients from the Vancouver and Kelowna Cancer Centers (CC) in British Columbia who were treated with Ra223 between June 2015 and December 2016 were identified. Patients completed the Brief Pain Inventory (BPI) just prior to each Ra223 injection. Pain response was defined as a two or more point improvement in worst pain relative to baseline, without an increase in pain medication level. ALP was determined at each visit, with a response threshold defined as a 30% decrease from baseline, consistent with the definition of response used in the ALSYMPCA trial.

Results: A total of 65 patients in Vancouver and Kelowna CC received Ra223 during the study period and 56 patients had at least one BPI record, of which 44 (79%) patients were assessable for change in worst pain. Of the assessable patients, 23 (52%, 95% confidence interval [CI] 38-67) had a pain response, although the use of concurrent external beam radiotherapy was a confounder in four cases. Of the 44 patients assessable for change in worst pain, 59% had ALP responses greater than 30%. An ALP response was seen in 56% of pain-responders vs. 43% of non-pain-responders. There was no association between pain response and ALP response (Phi =-0.05; p=0.77).

Conclusions: Ra223 administration was associated with a meaningful pain response rate in this cohort. There was no correlation between pain response and ALP response.