Use of bisphosphonates in metastatic breast cancer: single institution review at the Dr. H. Bliss Murphy Cancer Centre.

PURPOSE: Bone metastases occur in 65-75% of patients with metastatic breast cancer. These patients are at risk of developing skeletal-related events (SREs). SREs are defined as any pathological fracture, spinal cord compression, hypercalcemia, and surgery or radiation required for treatment of bone metastases. Bisphosphonates are used to prevent the development of SREs. The purpose of this study is to review the incidence of SREs in metastatic breast cancer patients with bony disease in Newfoundland and Labrador and to determine if there is an association between SREs and the type of bisphosphonate therapy given.

METHODS: This retrospective chart review includes all metastatic breast cancer patients with bony disease treated at the Dr. H. Bliss Murphy Cancer Centre from 2008 to 2010. Patient demographics, treatment received, and treatment changes were collected. Patients at the Centre received bisphosphonate, pamidronate or zolendronic acid to prevent SREs. The prescribing pattern of bisphosphonates was collected. The occurrences of SREs were then compared to the type of treatment received.

RESULTS: Sixty-five patients with breast cancer and bony metastasis were identified using the provincial tumor registry, three patients were excluded from the review as their charts could not be located. Following the initial diagnosis of bone metastasis, 8 patients (12.7%) were started on zolendronic acid, 50 patients (80.6%) were started on pamidronate, and 4 (6.4%) received no treatment. Six patients (75%) on zolendronic acid experienced one SRE; however, none experienced multiple SREs. Thirty-one patients (62%) on pamidronate experienced one SRE, and ten (20%) had multiple SREs. Of the 31 patients on pamidronate with an SRE, 4 (12.9%) were switched to zolendronic acid. Three of the four (75%) had multiple SREs despite treatment changes. Of the six patients on zolendronic acid with SREs, none were switched to pamidronate.

CONCLUSION: Our results show that the majority of patients with breast cancer, who develop bony metastases in Newfoundland and Labrador, are initially treated with the bisphosphonate, pamidronate. Over 60% of these patients experienced at least one SRE, and 20% had more than two SREs. A small proportion of the patients were initially started on zolendronic acid, and this group had better outcomes with fewer SREs and none had more than two SREs. It appears that zolendronic acid is superior to pamidronate in preventing SREs; however, zolendronic acid is being used primarily as second-line in Newfoundland and Labrador.