A Phase III randomized trial was designed to assess the effectiveness of samarium-153 (¹⁵³Sm)-lexidronam for palliation of bone pain in patients with hormone-refractory prostate cancer.

A total of 152 men with hormone-refractory prostate cancer and painful bone metastases were enrolled in a prospective, randomized, double-blind trial comparing radioactive (¹⁵³Sm) versus nonradioactive (¹⁵²Sm) lexidronam complexes. Patients were randomized (2:1) to the radioactive (¹⁵³Sm) agent. Patient diaries recording daily pain and analgesic use were completed during a planned 16-week evaluation period. Nonresponders were informed of the treatment received after 4 weeks of treatment and, if initially treated with placebo, were allowed to receive ¹⁵³Sm-lexidronam in an open-label fashion. Pain was measured using validated patient-derived visual analog scales and pain descriptor scales.

¹⁵³Sm-lexidronam had positive effects on measures of pain relief compared with placebo within 1 to 2 weeks. Reductions in opioid use were recorded at weeks 3 and 4. Because nonresponders were unblinded at week 4, statistical comparisons between the arms beyond week 4 were not possible. Mild, transient bone marrow suppression was the only adverse event associated with ¹⁵³Sm-lexidronam administration. The mean nadir white blood cell and platelet count (3 to 4 weeks after treatment) was 3800/μL and 127,000/μL, respectively. Counts recovered to baseline after approximately 8 weeks. No grade 4 decreases in either platelets or white bloods cells were documented.

These findings demonstrate that 1 mCi/kg ¹⁵³Sm-lexidronam is both safe and effective for the palliation of painful bone metastases in patients with hormone-refractory prostate cancer.