A phase II study of treatment of painful multifocal skeletal metastases with single and repeated dose samarium-153 ethylenediaminetetramethylene phosphonate

A phase II study of ¹⁵³Sm ethylenediaminetetramethylene phosphonate (¹⁵³Sm-EDTMP) palliative treatment was conducted on 23 patients with painful disseminated skeletal metastases. The administered activity of ¹⁵³Sm-EDTMP was determined by prospective dosimetry and the radiation absorbed dose to bone marrow was fixed at 2 Gy. Symptomatic relief of bone pain was experienced by 14 of 23 evaluable patients (61%) with a median duration of 8 weeks (range 0–40). Toxicity was limited to myelosuppression with median nadir counts of leucocytes 3.3 × 10⁹/l (range 1.0–7.5) and platelets 133 × 10⁹/l (range 24–176) occurring at 2 weeks and 4 weeks, respectively. Retreatment with ¹⁵³Sm-EDTMP was studied in 15 patients, including in 4 of the 23 patients treated with a single dose. The retreatment median radiation absorbed dose to red marrow was 1.9 Gy given at a median of 9 weeks (range 6–38) after initial treatment. Good control of pain was obtained in 13 of these patients (87%). Both the median duration of pain control (24 weeks) and survival (9 months) in the retreated group were substantially greater than for patients treated with a single dose, where duration was 8 weeks and survival 4 months. Additional toxicity in the retreated patients was confined to anaemia which required blood transfusion in 9 of the 15 patients (60%).