Purpose
The bone scan index (BSI) describes the tumor burden in bones as a percent of the total skeletal mass based on reference skeletal masses by bone scintigraphies. We conducted a prospective observational study to investigate the utility of BSI for breast cancer patients with bone metastasis.
Methods
We included patients with histologically or cytologically diagnosed breast cancer, radiologically or histologically confirmed bone metastasis, and receipt of less than three lines of systemic treatments. Bone scintigraphies were performed at the period of study enrollment and 12 and 24 weeks later. BSI was evaluated centrally. The primary endpoint was progression-free survival (PFS); secondary endpoints were overall survival (OS) and skeletal-related events.
Results
A total of 167 patients were enrolled and 153 were evaluable in the analysis. All the patients had bone metastasis; 45.8 % (n = 70) had bone-only disease, 17.0 % (n = 26) had lung, and 4.6 % (n = 7) had liver metastasis. The change in BSI from baseline to 12 weeks was significantly correlated with PFS (HR 1.25, 95%CI 1.13-1.40, p<0.01) and OS (HR 1.26, 95%CI 1.08-1.47, p<0.01). The change in BSI from baseline to 24 weeks was also significantly correlated with PFS (HR 1.32, 95%CI 1.06-1.65, p = 0.01) and OS (HR 1.47, 95%CI 1.11-1.95, p<0.01). The baseline BSI was not associated with PFS or OS.
Conclusion
Among the metastatic breast cancer patients with bone metastasis, BSI changes from baseline to 12 weeks and 24 weeks were significantly related with PFS and OS.