Is ¹⁵³Samarium-ethylene-diamine-tetramethyl-phosphonate (EDTMP) bone uptake influenced by bisphosphonates in patients with castration-resistant prostate cancer?

Objective: To evaluate the impact of biphosphonate administration on subsequent (153)Samarium-ethylene-diamine-tetramethyl-phosphonate (EDTMP) uptake in bone metastases of patients with castration-resistant prostate cancer.

Patients And Methods: The bone uptake of (153)Sm-EDTMP was assessed in 40 consecutive patients with castration-resistant prostate cancer and multiple painful bone metastases and no prior bisphosphonate therapy. (153)Sm-EDTMP was repeated after 3 months in the presence of bisphosphonates (zoledronic acid every 4 weeks, first administration 1 week after (153)Sm-EDTMP administration). The retained activity in bone was evaluated 20 h after application using whole-body scintigraphy (acquisition 15 cm/min).

Results: Mean patient age was 69 ± 4.8 years (range 57-77 years). Mean PSA level at study entry was 18.2 ± 21.0 ng/ml. (153)Sm-EDTMP uptake ranged from 36.3 to 75.3% (mean 55.1 ± 10.9%) before bisphosphonate administration and 35.6 to 73.3% (mean 55.2 ± 10.4%) after bisphosphonate administration. No significant intra-individual difference with or without bisphosphonate treatment was observed (P = 0.647).

Conclusions: Bisphosphonate treatment does not affect (153)Sm-EDTMP bone uptake in patients with castration-resistant metastatic prostate cancer. Thus, bisphosphonate treatment can be continued safely during samarium therapy.