Uptake of bone modifying agents in patients with HER2+ metastatic breast cancer with bone metastases - prospective data from a multi-site Australian registry.

Abstract

International practice guidelines recommend administration of bone modifying agents (BMA) in metastatic breast cancer (MBC) patients with bone metastases to reduce skeletal related events (SRE). Optimal delivery of BMA in routine clinical practice including agent selection and prescribing intervals remains unclear. We aim to describe real-world practice of Australian breast oncologists. Prospective data from February 2015 to July 2020 on BMA delivery to MBC patients with bone metastases was analysed from TABITHA, a multi-site Australian HER2+ MBC registry. Of 333 HER2+ MBC patients, 171 (51%) had bone metastases at diagnosis, with a mean age of 58.1 years [range 32-87]. 130 (76%) patients received a BMA, with 90 (69%) receiving denosumab and 40 (31%) receiving a bisphosphonate. Patients who received a BMA were more likely to have received concurrent first line systemic anti-HER2 therapy (95% vs 83%, p=0.04), to present with bone-only metastases at diagnosis (24% vs 7%, p=0.02) and less likely to have visceral metastases (51% vs 71%, p=0.03). Ten of 40 (25%) bisphosphonate patients and 45 of 90 (50%) denosumab patients received their BMA at the recommended 4-weekly interval. Prescribing intervals varied over time. Adverse events reported were consistent with clinical trial data. Three-quarters of Australian HER2+ MBC patients with bone metastases receive a BMA, often at different schedules than guidelines recommend. Further studies, including of all MBC subtypes, are warranted to better understand clinicians' prescribing rationale and potential consequences of current prescribing practice on SRE incidence. This article is protected by copyright. All rights reserved.