A phase IIa, nonrandomized study of radium-223 dichloride in advanced breast cancer patients with bone-dominant disease

Radium-223 dichloride (radium-223) mimics calcium and emits high-energy, short-range alpha-particles resulting in an antitumor effect on bone metastases. This open-label, phase IIa nonrandomized study investigated safety and short-term efficacy of radium-223 in breast cancer patients with bone-dominant disease. Twenty-three advanced breast cancer patients with progressive bone-dominant disease, and no longer candidates for further endocrine therapy, were to receive radium-223 (50 kBq/kg IV) every 4 weeks for 4 cycles. The coprimary end points were change in urinary N-telopeptide of type 1 (uNTX-1) and serum bone alkaline phosphatase (bALP) after 16 weeks of treatment. Exploratory end points included sequential ¹⁸F-fluorodeoxyglucose positron emission tomography and computed tomography (FDG PET/CT) to assess metabolic changes in osteoblastic bone metastases. Safety data were collected for all patients. Radium-223 significantly reduced uNTX-1 and bALP from baseline to end of treatment. Median uNTX-1 change was −10.1 nmol bone collagen equivalents/mmol creatinine (−32.8 %; P = 0.0124); median bALP change was −16.7 ng/mL (−42.0 %; P = 0.0045). Twenty of twenty-three patients had FDG PET/CT identifying 155 hypermetabolic osteoblastic bone lesions at baseline: 50 lesions showed metabolic decrease (≥25 % reduction of maximum standardized uptake value from baseline) after 2 radium-223 injections [32.3 % metabolic response rate (mRR) at week 9], persisting after the treatment period (41.5 % mRR at week 17). Radium-223 was safe and well tolerated. Radium-223 targets areas of increased bone metabolism and shows biological activity in advanced breast cancer patients with bone-dominant disease.