Rhenium-186-1,1-hydroxyethylidene diphosphonate (186Re-HEDP) has been used for the palliative treatment of metastatic bone pain. A Phase 1 dosage escalation study was performed using 186Re-HEDP in patients with metastatic breast cancer.
Methods: Twelve patients with metastatic breast cancer were studied. Each patient had at least four bone metastases and adequate hematological function. Groups of three consecutive patients were treated with dosages starting at 1295 MBq (35 mCi) and increasing to 2960 MBq (80 mCi) (escalated in increments of 555 MBq).
Results: A transient increase in pain ("flare" reaction) was observed in six patients. Two patients who received 2960 MBq 186Re-HEDP showed Grades 3 (platelets 25-50 x 10(9)/l) and 4 (platelets < 25 x 10(9)/l) platelet toxicity, which was defined as unacceptable. Prior to treatment, alkaline phosphatase levels were elevated in seven cases. These patients showed a transient decline in alkaline phosphatase levels during the first 4 wk.
Conclusion: The maximum tolerated administered activity of 186Re-HEDP in patients with metastatic breast cancer is 2405 MBq (65 mCi). Thrombocytopenia proved to be the dose-limiting toxicity, which could not be predicted adequately by the administered activity. Changes of alkaline phosphatase levels suggest anti-tumor effects of 186Re-HEDP.