Treatment Persistence With Monthly Zoledronic Acid is Associated With Lower Risk and Frequency of Skeletal Complications in Patients With Breast Cancer and Bone Metastasis

BackgroundZoledronic acid (ZA) reduces skeletal complications in breast cancer patients with bone metastases. This study explored relationships between ZA treatment persistence and patient outcomes.MethodsTwo thousand three hundred ninety-four female patients with breast cancer and bone metastasis were identified from the PharMetrics® Integrated Database between January 2003 and October 2006. Of these women, 714 (29.7%) received ZA; the remainder received no intravenous (IV) bisphosphonate (untreated). ZA treatment persistence was measured from first treatment to the first treatment gap > 45 days. Treatment persistence was categorized as short (≤ 90 days, n = 230), medium (91-180 days, n = 171), or long (> 180 days, n = 313). Relationships between ZA treatment and persistence on outcomes were assessed in regression models adjusted for age, comorbidities, and propensity to receive treatment.ResultsCompared with untreated patients, after multivariate adjustment, ZA-treated patients experienced a 25% lower rate of skeletal complications (P < .05), were at lower risk for skeletal complications or loss to follow-up (hazard ratio [HR] = 0.67; P < .001), and had 41% longer follow-up time (P < .001). The skeletal complication risk was lower in the long-persistence group than in the short-persistence group (HR = 0.576; P < .05). In patients with ≥ 1 skeletal complication, the long-persistence group had 39% fewer skeletal complications than the short-persistence group (P < .01). The medium- and long-persistence groups had 40% and 139% longer follow-up than the short-persistence group (both P < .001).ConclusionsZA treatment was associated with lower risk and frequency of skeletal complications and longer follow-up time. Greater persistence with ZA treatment was associated with better outcomes.