(89)Sr imaging with bremsstrahlung in patients with metastatic breast cancer

In this study, we investigated the clinical and laboratory factors that may enhance (89)Sr uptake to strengthen its tumoricidal effect.

We enrolled 21 patients with multiple bone metastases (n = 23) from breast cancer and classified them into 2 groups according to their zoledronic acid (ZOL) treatment history. (89)Sr imaging with bremsstrahlung was performed 2 to 6 weeks after administration and (89)Sr index was measured using combined imaging with bone scintigraphy. We compared the Sr index with the levels of alkaline phosphatase, bone-specific alkaline phosphatase, serum cross-linked N-telopeptides, carboxy-terminal telopeptide of type 1 collagen, C-reactive protein, calcium, and hemoglobin on administration and evaluated the differences among the groups.

The (89)Sr index ranged from 0.01 to 2.0 and was significantly correlated with C-reactive protein and alkaline phosphatase and moderately correlated with carboxy-terminal telopeptide of type 1 collagen, serum cross-linked N-telopeptides, and bone-specific alkaline phosphatase. The (89)Sr index was not significantly correlated with calcium or hemoglobin. The group with less than 1 year of ZOL treatment demonstrated a mean (SD) (89)Sr index of 1.11 (0.59), and the group with 1 or more years of ZOL treatment showed a mean (89)Sr index of 0.36 (0.26). The Wilcoxon signed-rank test demonstrated a significant difference between the 2 groups (P < 0.001).

(89)Sr accumulation seemed to be associated with bone turnover, in particular bone resorption, and vascularization due to inflammation or tumor growth. Long-term ZOL treatment may reduce bone resorption and vascularization. To enhance the tumoricidal effect and palliation of bone pain by (89)Sr, combined therapy must be established.