Long‐term Treatment with Intravenous Bisphosphonates in Metastatic Breast Cancer: A Retrospective Study

Bisphosphonates are important therapies used to reduce the risk of skeletal‐related events in patients with bone metastases from breast cancer (BC). This retrospective cohort study evaluated the incidence of osteonecrosis of the jaw (ONJ) and renal impairment in women (n = 221) with bone metastases from BC treated with intravenous bisphosphonates from January 1999 to June 2008. In the long‐term cohort, 159 patients received pamidronate (n = 9), zoledronic acid (n = 110), or both (n = 40) for ≥24 months. The comparator group consisted of patients treated with intravenous bisphosphonates for 12–23 months (n = 62). After 39 months' median follow‐up, six of 159 patients developed ONJ (3.8%; median 38.5 treatment cycles and 44 months' exposure) in the long‐term cohort. Of patients who developed ONJ, 50% resumed intravenous bisphosphonates after a 12‐month treatment holiday. Renal impairment developed in 19 patients in the long‐term cohort (11.9%; median 26 treatment cycles and 26 months' exposure). Of these 19 patients, 11 (57.9%) recovered baseline renal function and seven (36.7%) showed partial recovery. After modification of the intravenous bisphosphonate regimen, 17 of 19 patients (89.4%) resumed therapy. Of the 62 patients in the comparator cohort, one patient developed ONJ (1.6%) and six developed renal impairment (9.7%). Similar incidence rates of ONJ and renal impairment were observed for the long‐term and comparator cohorts. Times to ONJ or renal impairment also were similar across intravenous bisphosphonate type. Long‐term (≥24 months) intravenous bisphosphonate use in metastatic BC is well tolerated, with low incidences of ONJ and renal impairment.