Incidence of hypocalcemia in patients with castration-resistant prostate cancer treated with denosumab: Data from a non-inferiority phase III trial assessing prevention of symptomatic skeletal events (SSE) with denosumab administered every four weeks (q4w) versus every 12 weeks (q12w)—SAKK 96/12 (REDUSE).

139Background: DN given q4w has shown superiority in delaying skeletal related events over q4w zoledronic acid (ZA). Recently it has been demonstrated that ZA q12w is non-inferior to ZA q4w. The objective of REDUSE is to show non-inferiority for DN q12w versus q4w in terms of SSE. Here we present an interim analysis for the secondary endpoint HC. Methods: Patients (pts) with castration resistant prostate cancer (planned N=690) were randomized 1:1 to DN q4w (Arm A) vs q12w (Arm B) after a 16 week induction phase with application q4w. All pts received vitamin D (ViD) 400 U and calcium (Ca) 500 mg daily. Measurement of corrected serum-Ca was mandatory before each DN injection. This interim analysis was performed after 3.5 years of accrual. Men who received ≥ 1 dose of DN were considered evaluable. Results: 383 pts were evaluable. HC occurred in 28.7% during the first 16 weeks (DN q4w for all pts) and 30.2% afterwards. After the induction phase HC occurred in 40.2% in Arm A and in 20.3% in Arm B. Grade 3 (2.1...