Bisphosphonates are strongly efficacious in inhibiting osteoclast bone resorption and have beneficial effects on bone metastasis. Due to their mechanism of action, bisphosphonates are expected to prevent the development of bone metastases in breast cancer patients. Pamidronate is a potent inhibitor of osteoclast activity. We examined whether pamidronate was able to prevent the development of bone metastases in breast cancer patients at high risk for bone metastasis. Between 1997 and 2001, 90 patients with primary breast cancer with ≥4 positive nodes were assigned to receive 45 mg pamidronate 4 times every 2 weeks (33 patients) or standard follow-up (57 patients) based on patient self-preference. Patients underwent surgery and adjuvant therapy. The characteristics of the patients in the two groups were well-balanced. The median follow-up period was 5 years. Bone metastases were detected in 12.1% of patients in the pamidronate group and 40.4% in the control group (p=0.005). Distant metastases (36.4 vs. 56.1%, p=0.071) and non-osseous metastases (33.3 vs. 52.6%, p=0.077) were detected at a lower frequency in the pamidronate group. Thus, the rate of bone metastasis-free survival was significantly higher in the pamidronate group (85.9 vs. 64.0% at 5 years, p=0.023). Overall and disease-free survival rates did not differ between the two groups. In the pamidronate group, the incidence of bone metastases was significantly reduced and bone metastasis-free survival was significantly higher. Adjuvant pamidronate therapy therefore prevents the development of bone metastases in breast cancer patients with ≥4 positive nodes.

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