Evaluation of prescribing practices of denosumab and zoledronic acid in breast and prostate cancer patients at University of Chicago Medicine.

Abstract

e24144 Background: Zoledronic acid (ZA) and denosumab are both bone-modifying agents (BMAs) approved for use in patients with bone metastases with breast or prostate cancer as well as patients who are receiving aromatase inhibitors (breast cancer) or androgen deprivation therapy (prostate cancer). There are various frequencies of administration, doses, and duration of these agents depending on indication and extent of disease. Currently there is data to show that ZA can be given every 3 months in patients with metastatic breast and prostate cancer, however, there is no data that clearly indicates that denosumab every 3 months is non-inferior to every 28 days. This study aimed to analyze current prescribing patterns of ZA and denosumab in metastatic breast cancer and metastatic castration resistant prostate cancer patients at The University of Chicago Medicine (UCM). Methods: This was a retrospective study of 80 patients who received at least one dose of ZA or denosumab between July 1st 2018 to June 30th 2019 from UCM outpatient oncology clinic for the purpose of treating metastatic breast cancer or metastatic castration resistant prostate cancer in conjunction with standard antineoplastic therapy. All included patients must have bone metastases. Patients were divided into four groups by disease state (breast or prostate cancer) and BMA agent (ZA or denosumab). The primary outcome was BMA therapy adherence rate, which was defined by those who received greater than or equal to 80% of appropriately scheduled doses. Descriptive statistics were used for skeletal-related events (SREs) and BMA associated adverse effects. Results: Patients who received ZA achieved higher adherence rates (100% breast, 86% prostate) compared to patients that received denosumab (63% breast, 23% prostate). The most common reason for the lower adherence rate in denosumab groups was scheduling convenience. During the study period, there were 3, 0, 2 and 5 patients had SREs in the above four groups respectively. The predominant adverse event across all groups was hypocalcemia and two patients with prostate cancer on denosumab developed osteonecrosis of the jaw. The cost analysis showed using ZA as primary BMA agent might save up to 2.5 million dollars per year at UCM. Conclusions: The use ofZA was associated with higher adherence rates compared to denosumab. Implementing a pharmacy driven protocol for ZA use for patients with metastatic breast and prostate cancer may improve BMA regimen adherence rates and significantly reduce costs.