A randomized trial comparing four-weekly versus 12-weekly administration of bone-targeted agents (denosumab, zoledronate, or pamidronate) in patients with bone metastases from either breast or castration-resistant prostate cancer.

11501 Background: Defining the optimal dosing interval of commonly used bone-targeted agents (BTAs), such as denosumab and bisphosphonates, for patients with bone metastases remains an important clinical question. We performed a pragmatic randomised trial comparing the non-inferiority of 12- versus 4-weekly BTAs in patients with bone metastases from breast and prostate cancer. Methods: Patients with bone metastases, who were either BTA-naïve, or already receiving, denosumab, pamidronate or zoledronate were eligible. They were randomised to receive their chosen BTA every 12- or 4-weeks for one year. The primary endpoint was Health related quality of life (HRQL) (EORTC-QLQ-C30 Functional Domain - Physical Subdomain). Secondary endpoints included: pain (EORTC-QLQ-BM22 - pain domain), Global Health Status (EORTC-QLQ-C30), symptomatic skeletal events (SSE) rates and time to SSEs. Adverse events and toxicity profiles were also compared. Results: Of 263 patients (60.8% breast and 39.2% prostate), 130 (49.4%) were randomised to 12-weekly and 133 (50.6%) to 4-weekly therapy. 138 (52.5%) were bone-agent naïve. The BTAs included; denosumab (n=148, 56.3%), zoledronate (n=63, 24.0%) and pamidronate (n=52, 19.8%). Study-reported outcomes showed no significant difference in; HRQL-physical domain (median [range]: 0 [-86, 40] vs. 0 [-66, 53.3]), pain (median [range]: 0 [-66, 72] vs. 0 [-100, 88]), Global Health Status (median [range]: 0 [-100, 66.7] vs. 0 [-83, 33.3]), SSE rates (N [%]: 24 [18.5%] vs. 22 [16.5%]), 1-year SSE-free rate (median, range; 73.2% [63.6, 80.7] vs. 77.9% [69.1, 84.4]) between the 12- and 4-weekly arms, respectively. Subgroup analyses for BTA naïve and pre-treated patients, and for patients receiving denosumab, zoledronate and pamidronate, showed no significant difference between the 12- and 4-weekly arms. There was no significant difference in reported rates of renal impairment (2.3% vs. 3.0%), symptomatic hypocalcaemia (1.5% vs. 1.5%) or osteonecrosis of the jaw (0.8% vs. 0.8%). Conclusion: The findings of this trial are consistent with those previously reported for de-escalating zoledronate. This trial also included patients receiving de-escalated denosumab and pamidronate. While the results of the Swiss REDUSE trial are awaited, the data presented would suggest that de-escalation of all commonly used BTAs is a reasonable treatment option. Clinical trial information: NCT02721433.