Double blind dose ranging study of strontium-89 chloride in bone metastases associated with breast cancer

Strontium-89 chloride was evaluated at four doses in 140 patients with painful bony metastases due to breast cancer (median age 54 years). Females were selected with an anticipated life expectancy of six months, WHO index =2 and predominantly skeletal metastatic disease. Major exclusions were inadequate hepatic or renal function, hypercalcaemia impending fracture, cord compression or concomitant disease causing skeletal pain. Patients were randomly assigned a single intravenous injection of: 20μCi/kg lean bodyweight (0.74 MBq/kg), 40μCi/kg (1.48MBq/kg), 60μCi/kg (2.22MBq/kg) or 80μCi/kg (2.96MBq/kg), and followed for six months. Painful metastatic sites were confirmed scintigraphically, and pain was assessed at each, using a four point scale for severity and frequency, at three-weekly intervals for three months, then six-weekly to six months. Patients recorded analgesic consumption in daily diary cards. Pain scores were reduced compared with baseline for all doses. For all but the lowest dose, severity was typically reduced from moderate/severe at baseline to mild/moderate by Week 9. At Week 12, these effects were significantly greater for the higher dose groups than for the 20μCi/kg dose group. By Week 9, 21 % of patients had reduced analgesic consumption, and 59% were classed as responders (observed reduction in pain severity, pain frequency or analgesic consumption without concurrent increase in other measures). The effects were maintained to Week 24. Consistent with other studies of strontium-89 chloride there was a reduction in platelet and WBC counts occurring between 6 and 9 weeks after injection. Nadirs were rarely clinically significant. The treatment was effective and well tolerated at doses up to 80μCi/kg.