Bone modifying agents for patients with bone metastases from breast cancer managed in routine practice setting:...

Bone metastases are common in patients with breast cancer and can lead to pain and skeletal-related events. Bone modifying agents are licensed to be used for these patients. We report the treatment patterns and outcome of zoledronic acid and denosumab in routine practice.

Women with bone metastases from breast cancer who have started denosumab or zoledronic acid between 2011 and 2016 were eligible. Those with history of bone modifying agent use prior to diagnosis of bone metastases or with switching treatment between zoledronic acid and denosumab were excluded. Details of patients, tumors, bone modifying agent treatment, selected bone modifying agent toxicity, time to skeletal-related event development, and overall survival were collected retrospectively.

In total, 163 women were eligible and included in this analysis. Number of skeletal-related events prior to starting bone modifying agents was 0, 1, 2, and 3 in 91 (55.8%), 53 (32.5%), 13 (8%), and 6 (3.7%), respectively. Zoledronic acid was started for 107 (65.6%) and denosumab for 56 (34.4%) patients. The proportion of patients receiving denosumab increased from 23.1 to 54.3% in years 2011 and 2016, respectively. Dose delay, reduction, and discontinuation due to toxicity were reported more frequently in patients receiving zoledronic acid. Denosumab delayed time to first on-treatment skeletal-related event compared with zoledronic acid (hazard ratio, 0.64; 95% CI, 0.41-0.98; log rank P = 0.044). There was no significant difference in median survival (zoledronic acid: 62 and denosumab: 58 months; log rank P = 0.956).

Denosumab is superior to zoledronic acid in reducing risk of skeletal-related events and in tolerance profile. However, overall survival is similar with both treatments. Our findings mirror those reported in scrutinized environment of landmark clinical trials.