Osteonecrosis of the jaw (ONJ) in radium 223 (Ra223)-treated metastatic castration-resistant prostate cancer (mCRPC) patients (pts) with exposure to zoledronic acid and/or denosumab.

Abstract

5575 Background: Bone health agents (BHA) including denosumab, a monoclonal antibody, and Zoledronic acid (ZA), a bisphosphonate, are recommended for men with CRPC and bone metastases to prevent skeletal-related complications. ONJ occurs in about 5% of patients (pts) on BHA. The incidence of ONJ in pts treated with Ra223 and BHA remains unknown, particularly in those who receive sequential treatment of BHAs. Here we describe the rate of ONJ in a real-world setting in mCRPC pts treated with Ra223 in 3 groups: 1) denosumab alone, 2) ZA alone, and 3) sequential ZA /denosumab or vice versa. Methods: A retrospective analysis of a cohort of mCRPC pts with bone metastases who received Ra223. Follow-up was until date of death or last data entry. Chart inclusion criteria included patients who received Ra223 between November 2010 to August 2018 with documentations of data points. Results: A total of 177 pts received Ra223 between 11/2010 and 8/2018. Median age 73 at 1st Ra223 (range 40-93); Median PSA 15.8- at 1st Ra223 (range 0.1-1952); Demographics-AA-10, C-130, Asian-9, unspecified-28; Median Alk Phos 95 at 1st Ra233 (range 25-1515). 93 % (164/177) received BHA. Of the 164 who received BHA, 45% (73/164) received denosumab only, 37% (61/164) received ZA only, and 18% (30/164) received sequential treatment. ONJ developed in 9.7% (16/164) of all patients on BHA. Denosumab alone caused ONJ in 7 of 73 pts (9.6%). ZA alone caused ONJ in 6 of 61 pts (9.8%). ONJ occurred in 3 of 30 pts (10%) in the sequential group. The median number of doses of BHA before development of ONJ was 10 with denosumab, 20 with ZA, and 19.5 (denosumab) and 22 (ZA) in the sequential group. Conclusions: In patients treated with Ra223 and a BHA, the rate of ONJ is 9.7%. The rate of ONJ was similar in groups treated with denosumab alone, ZA alone, and sequential treatment of ZA and denosumab However, ONJ developed more quickly in patients on denosumab. We conclude that the risk of ONJ is increased in patients treated with Ra223 and BHA. ZA or sequential therapy appears to delay time to onset of ONJ compared to denosumab. Clinicians should be mindful of the toxic synergy between Ra223 and BHA. ZA may be the preferred BHA partner with Ra223.