Evaluation of tartrate-resistant acid phosphatase (TRAP) 5b as serum marker of bone metastases in human breast cancer.

Background: The osteoclast-specific active TRAP 5b isoform is detectable in serum and claimed to be a specific marker of bone resorption. The present study was undertaken to evaluate the usefulness of TRAP 5b as a serum marker of bone resorption in breast cancer patients with bone metastases.
Materials and Methods: TRAP 5b serum levels were measured in 192 samples from patients with breast cancer with and without bone metastases and in 53 healthy pre- and postmenopausal women using the enzyme immunoassay Bone-TRAP.
Results: Serum levels of TRAP 5b were significantly higher in patients with breast cancer and clinical signs of bone metastases before therapy than in healthy women. There was also a significant difference between patients with bone metastases before and during bisphosphonate therapy, indicating a reduction of bone alteration under this treatment. The subgroup with progression of bone metastases under bisphosphonate therapy showed the highest difference in TRAP 5b concentrations compared to patients with stable disease.
Conclusion: Serum TRAP 5b levels are elevated in patients with bone metastases and breast cancer. The TRAP 5b levels decline under bisphosphonate therapy when no progression is detectable. When progress of the bone metastases occurs, TRAP 5b levels rise again. Therefore, active TRAP 5b seems to be a useful serum marker for bone metastases in breast cancer patients, especially to detect progressive disease under bisphosphonate treatment. Further studies with larger numbers of patients are required to confirm these data.