1513PRISK FACTORS FOR HYPOCALCEMIA IN PATIENTS WITH CANCER RECEIVING DENOSUMAB

Abstract Aim: The potent RANK ligand inhibitor denosumab (Dmab) can cause hypocalcemia (hypoCa). Patients (pts) with inadequate intake of Ca and vitamin D are at increased risk for hypoCa. Additional baseline risk factors for hypoCa in pts with metastatic bone disease (MBD) were evaluated to aid clinical risk assessment for this adverse event. Methods: A post hoc analysis used data from three identically designed, randomized, blinded phase 3 trials comparing monthly dosing of 4 mg zoledronic acid (ZA) to 120 mg Dmab in pts with MBD to identify lab events of grade≥2 hypoCa (CTCAE:median (20.77 μg/L)2.078(1.579, 2.734)median vs≤median> 2 bone mets4.236(2.117, 8.479)≤ 2 bone mets1.773(1.312, 2.395)Interaction of baseline BSAP and # of bone mets0.021uNTX>50 nmol/mmol1.316(1.031, 1.680)0.027Interaction of baseline uNTX and # of bone mets0.21 Conclusions: The risk of hypoCa after Dmab for MBD is associated with the # of bone mets and elevated bone turnover markers, especially high BSAP with>2 mets. BSAP may indicate the potential for deposition of Ca in undermineralized matrix. Pts with high bone turnover may be more susceptible to hypoCa when osteoclasts are rapidly inhibited, particularly when Ca and vitamin D intake is insufficient. Disclosure: J. Body: Consultant for and received research funding from Amgen; received honoraria from Amgen and Novartis; H.G. Bone: Consultant for and received honoraria from Amgen and Novartis; C. van Poznak: Received research funding from A