Real-world uptake of bone modifying agents in advanced breast cancer with bone metastases-Prospective data from a multi-site Australian registry

Abstract

Background and Aim: International practice guidelines recommend use of bone-modifying agents (BMA) in advanced breast cancer (ABC) patients with bone metastases, to reduce the frequency of bone metastases and delay the onset of skeletal-related events. However, delivery of BMA in routine clinical practice, including the timing of initiation, frequency of administration and monitoring of side effects is largely unknown. To improve understanding of BMA prescribing patterns, we aim to describe the real-world practice of Australian clinicians. Method(s): Prospective data from February 2015 to July 2020 on BMA delivery to ABC patients with bone metastases, was analysed from TABITHA, a multi-site Australian HER2+ ABC registry. Result(s): Of 333 HER2+ABC patients, 183 (55%) had bone metastases. Mean age was 58.1 [range 32-87 years], 125 (68%) were oestrogenreceptor positive. 136/183 (74%) patients received BMA at any line. 119/136 (88%) commencedBMAin the first-line setting. 29/136 (21%) patients received bisphosphonates with 2 (7%) receiving monthly dosing. 95/136 (70%) patients received denosumab with 28 (30%) receiving monthly dosing. Additional documented bone health interventions including exercise (10/136, 7%), vitamin D (13/136, 10%) and calcium (60/136, 44%) were reported. BMA associated hypocalcaemia occurred in 9/136 (7%), osteonecrosis of the jaw in 3/136 (2%). Of the 47 (26%) patientswho did not receive BMA, 17 included clinician rationale. The most common reason reported was low volume disease in 6 patients. Conclusion(s): Whilst denosumab appears to be favoured by clinicians over bisphosphonates, and the majority of patients started treatment in the first-line setting, one-quarter of ABC patients with bone metastases do not receive a BMA. Despite initial landmark trials reporting monthly administration of BMA, a minority of patients remain on this frequency. BMA associated complications remain low, consistent with trial data. Further studies arewarranted to investigate clinicians' rationale on BMA initiation and selection.