Treatment persistence with monthly zoledronic acid is associated with lower risk and frequency of skeletal complications in patients with breast cancer and bone metastasis

Background: Zoledronic acid (ZA) reduces skeletal complications in breast cancer patients with bone metastases. This study explored relationships between ZA treatment persistence and patient outcomes. Methods: Two 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. Results: Compared 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 mediumand long-persistence groups had 40% and 139% longer follow-up than the short-persistence group (both P < .001). Conclusions: ZA 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.