The study covered in this summary was published on researchsquare.com as a preprint and has not yet been peer reviewed.

Key Takeaway

• In patients with HR-positive bone-metastatic breast cancer, a pooled analysis of two trials showed a trend favoring radium-223 plus endocrine therapy compared with endocrine therapy alone for bone-related endpoints but not for progression-free or survival endpoints.

Why This Matters

• Most women with advanced breast cancer experience skeletal metastases, which puts them at increased risk for bone-related events that can impair quality of life.

• Radium-223 selectively targets areas of bone metastases.

Study Design

• Researchers pooled analyses from two double-blind, placebo-controlled studies that explored whether adding radium-223 to endocrine therapy for women with HR-positive bone-metastatic breast cancer improved bone-related endpoints.

• Patients in study A received investigator’s choice of single-agent endocrine therapy; patients in study B received exemestane plus everolimus.

• Overall, 382 patients were randomly assigned to receive either radium-223 or placebo every 4 weeks for a total of six doses.

Key Results

• The median skeletal event-free survival was 22.2 months in the radium-223 arm, vs 19.9 months in the placebo arm — a nonsignificant difference (hazard ratio [HR], 0.81; P = .1389).

• However, patients in the radium-223 group did experience significant improvements in time to bone alkaline phosphatase progression (HR, 0.593; P = .0195).

• Radiographic progression-free survival and overall survival were not significantly different between the two groups (HR, 0.956; P = .704; and HR, 0.89; P = .441, respectively).

• Treatment-emergent adverse events were reported in more than half of patients in the radium-223 arm (50.3%), vs more than one third (35%) of patients in the placebo arm. The rate of grade 3 and 4 events was also higher in the radium-223 arm (25.7% vs 8.5%).

Limitations

• There were differences in study design between the two groups, including differences in endocrine regimens and variations in the duration of follow-up.

• Enrollment was stopped early in both studies, which decreased the sample size.

• Alkaline phosphatase measurements may have been missed.

Disclosures

• The study was supported by Bayer HealthCare.

This is a summary of a preprint research study, “Radium-223 in Women With Hormone Receptor-Positive Bone-Metastatic Breast Cancer Receiving Endocrine Therapy: Pooled Analysis of Two International, Phase 2, Randomized, Double-Blind, Placebo-Controlled Trials.” The study has not been peer reviewed. The full text can be found at researchsquare.com.

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