Safety and efficacy of bisphosphonates beyond 24 months in cancer patients

Purpose: Bisphosphonate therapy has decreased the risk of skeletal complications associated with osteolytic bone lesions in patients with breast cancer and multiple myeloma. The large prospective studies have used 21 to 24 months of treatment. We studied the safety and efficacy of bisphosphonates in a subset of patients who received therapy for more than 24 months. Patients and Methods: Patients who received bisphosphonates (pamidronate or zoledronic acid) were identified. Data on skeletal events and laboratory parameters were gathered by chart review. Results: We studied 22 patients who received intravenous pamidronate or zoledronic acid for a duration of 3.6 years (range, 2.2 to 6.0 years). Prolonged therapy was well tolerated. No significant calcium, phosphorus, electrolyte, or WBC count abnormalities were encountered. There was a clinically insignificant decrease in hemoglobin and platelet count and an increase in creatinine in these patients. The fracture rate beyond 2 years was no greater than during the first 2 years of treatment. There were no stress fractures of long bones with prolonged therapy. Conclusion: Prolonged treatment with the potent bisphosphonates pamidronate and zoledronic acid seems to be well tolerated and should be studied in prospective, randomized studies to document prolonged skeletal efficacy.