Abstract PS14-18: A physician survey evaluating real-world practice patterns and attitudes towards de-escalation of bone-modifying agents in patients with bone metastases from breast cancer
Authors: Alzahrani Mashari , Clemons Mark , Vandermeer Lisa , Sienkiewicz Marta , Awan Arif , Hutton Brian , Pond Gregory , Ng Terry 
Published: February 2021

Abstract
Background: Despite extensive use of bone modifying agents (BMA) in patients with bone metastases from breast cancer (BC), the optimal choice, frequency, and duration of BMA treatment remains unclear. A physician survey was performed to identify current practices and attitudes towards performing trials of de-escalation after 2 years of treatment, where very little prospective data exists.
Methods: Canadian oncologists treating breast cancer were surveyed from May to June 2020 via an anonymized online survey. Physicians were approached by e-mail invitation, and a follow-up e-mail was sent 2 weeks later. The study was approved by the Ontario Cancer Research Ethics Board. The survey collected physician demographics, current practice patterns, perception on risk of symptomatic skeletal events (SSE) and BMA-associated toxicity. It also assessed attitudes towards conducting a study evaluating further de-escalation of BMAs after 2 years of treatment.
Results: Of 238 potentially eligible breast oncologists on initial screening, 40 responded (response rate 16.8%; 97.5% medical oncologist). The most common BMA regimens during the first 2 years in patients with no limitations in drug coverage were denosumab q4wks for 3-4 months then q12wks [13/40 physicians (32.5%)], denosumab q4wks [7/40 (17.5%)], and zoledronate q12wks [8/40 (20%)]. For patients with no public funding for denosumab, the most common regimens were zoledronate q4wks for 3-4 months then q12wks [14/40 (35%)] and zoledronate q12wks [12/40 (30%)]. Most physicians [33/40 (82.5%)] routinely de-escalated BMA, with the most common approaches being de-escalation from the start of treatment [9/33 (27.3%)], after 3 months [7/33 (21.2%)], 6 months [6/33 (18.2%)], or 12 months [5/33 (15.2%)]. In terms of continuing BMA after 2 years, 11/40 (27.5%) felt there was benefit, 5/40 (12.5%) felt there was no benefit, and 24/40 (60%) were unsure. There was no consensus on the perceived risk of SSE or BMA-related toxicity after ≥ 2 years of BMA in breast cancer. Most physicians treating breast cancer-related bone metastases felt a de-escalation study after more than 2 years of BMA would be clinically important [i.v. bisphosphonate (BP) q12wks vs q24wks: 65%; i.v. BP q12wks vs. discontinue: 70%; denosumab q12wks vs q24wks: 57.5%; denosumab q12wks vs. discontinue: 67.5%]. Most physicians would accept SSE rate increase of &lt; 5% with BMA de-escalation. If a study of BMA de-escalation showing non-inferiority in terms of SSE rate was not feasible, physicians would consider changing practice to de-escalated therapy if: BMA toxicity was reduced (64.1%), pain was no worse (48.7%), physical function was no worse (48.7%), or cost-utility or cost-effectiveness was improved (41%). 38.5% would only change practice if the SSE rate was not significantly worse.
Conclusion: Despite their extensive use and costs, questions around optimal use of BMAs still exist. It is evident that practice varies according to patient insurance coverage, however most physicians are de-escalating BMAs. There is interest amongst clinicians in performing trials of de-escalation, especially after 2 years of treatment.
Citation Format: Mashari Alzahrani, Mark Clemons, Lisa Vandermeer, Marta Sienkiewicz, Arif Awan, Brian Hutton, Gregory Pond, Terry Ng. A physician survey evaluating real-world practice patterns and attitudes towards de-escalation of bone-modifying agents in patients with bone metastases from breast cancer [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS14-18.