PSAT164 Incidence and Severity of Hypocalcemia in Association with Antiresorptive Therapy in Cancer Patients with Bone Metastasis: An Integrated Health Network Experience

Abstract Introduction Antiresorptive therapy (ArT) has been known to decrease the risk of skeletal-related events (SRE), such as bone pain and pathological fractures, in cancer patients with bone metastasis (BM). While beneficial, ArT may cause adverse effects in this population including hypocalcemia, which can be severe and life-threatening. We examined the incidence, severity, and risk factors for hypocalcemia associated with the use of ArT to treat BM in cancer patients. Methods We conducted a retrospective review of the electronic medical records of adult patients with advanced cancer complicated by BM who were treated at our institution between January 2016 and November 2020. Our primary aim was to compare the incidence and severity of hypocalcemia with the use of IV Zoledronic acid (ZA), a bisphosphonate, vs SQ Denosumab (DM), a RANKL inhibitor, to treat BM in cancer patients.Our secondary aim was to compare risk factors associated with severe hypocalcemia (defined as albumin-corrected serum calcium < 7 mg/dL). Inclusion criteria were patients aged 19-99 years with a history of cancer with known BM, who received either ZA or DM. Results We reviewed 860 EMRs of patients treated within the specified period. 392 patients met inclusion criteria, among them, 297 (76%) and 95 (24%) received DM and ZA, respectively. There were no between-group differences in age, ethnicity, or weight. The median patient age was 71 years (range: 27–96). There were, however, between-group differences in gender (p=0.01) and cancer diagnoses (p=0.03). Females comprised 53.9% of the DM group vs. 40% of the ZA group. The top three cancer diagnoses were (DM vs ZA groups): breast (40.1% vs 26.3%), prostate (25.9% vs 40%), and lung cancer (17.8% vs 15.8%). Overall incidence of hypocalcemia was 48.8% (n=144) and 45.3% (n= 43) with the use of DM and ZA, respectively (p=NS). Severe hypocalcemia was more frequently observed with the use of DM vs ZA (6.6% vs 1.1%, p <0.05). Median (IQR) corrected serum calcium concentration following ArT (when trending calcium for the individual patient) was 8.4 (7.9-8.8) and 8.6 (8.2-8.8) mg/dL for DM a ZA groups, respectively (p=0.1). There were no between-group differences in risk factors for hypocalcemia, such as renal function (eGFR), concentrations of 25-hydroxy vitamin D, albumin, phosphorus, magnesium, or TSH. However, there was a between-group difference in the concentration of alkaline phosphatase (median 83 vs 101 IU/L for DM vs ZA, p= 0.02). There were no between-group differences in the type of BM (osteolytic vs osteoblastic, p=0.9) Conclusion: Severe hypocalcemia was significantly more common with the use of DM compared to ZA for the treatment of BM in cancer patients treated at our institution. Our study was limited by its retrospective design and the between-group differences in gender distribution and cancer diagnoses. Presentation: Saturday, June 11, 2022 1:00 p.m. - 3:00 p.m.