Correlations between activity of tartrate-resistant acid phosphatase-5b and whole body bone scan in patients of breast cancer with bony metastases

Objective: Tartrate-resistant acid phosphatase 5b (TRAP-5b) is a novel marker for evaluating osteoclastic activity and rate of bone resorption. The study observed the changes of circulating TRAP-5b activity and findings of bone scans in breast cancer patients with suspicious bony metastases. Methods: A total of 34 breast cancer patients with suspicious bony metastases were studied. Blood sampling and Tc-99m MDP (20mCi) whole body scans were performed at the same time. Specimens were stored at -70 and were simultaneously analyzed for activity of circulating TRAP-5b using a home-made EIA method (normal reference value: <3 U/L). Numbers of lesions (NL) found in bone scans were counted from imaging films. The NL were further divided into 2 categories: the limited lesion (NL 3) and extended lesion (NL > 3) groups. Results: Six patients revealed limited lesions (LL) and the other 28 revealed extended lesions (EL). Of the 34 patients, 20 received repeated bone scans which showed 7 in regression and 13 in progression of the bony lesions after anti-cancer treatment. The activity of TRAP-5b decreased significantly in regression group (mean±SD, 4.05±0.81 vs. 2.36±0.88 U/L; P<0.01) but not changed apparently in progression group (5.39±2.37 vs. 5.58±2.08 U/L). The TRAP-5b activity, however, significantly correlated with NL seen on bone scan (r= 0.52, P<0.01). Conclusion: TRAP-5b might be a suitable marker to evaluate status of bony metastases in patients with breast cancer and might also provide a reference to therapeutic response in this patient group