Different patterns of change in bone turnover markers during treatment with bone-modifying agents for breast cancer...

Bone-modifying agents are effective for treatment of breast cancer patients with bone metastases. Since their action is mediated through suppression of the osteoclast function, their efficacy can be determined by monitoring bone turnover markers. However, the clinical significance of these markers is yet to be compared.

For this study, 52 breast cancer patients with bone metastases treated with zoledronic acid (n = 36) or denosumab (n = 22) were enrolled (6 patients were treated sequentially with both agents). Serum tartrate-resistant acid phosphatase-5b (TRACP-5b), pyridinoline cross-linked carboxyterminal telopeptide of type I collagen (1CTP), N-terminal cross-linking telopeptides of type I collagen (NTX) and bone-specific alkaline phosphatase (BAP) were measured at pretreatment and 1, 3 and 6 months after treatment.

Serum TRACP-5b (p < 0.0001), NTX (p = 0.0007) and BAP (p = 0.0032) decreased significantly after treatment. The baseline median value of TRACP-5b (457.5 mU/dL, range 173-1630 mU/dL) decreased to 137 mU/dL (91-795 mU/dL) 1 month after treatment. Reduction in serum NTX and BAP was greatest after 3 and 6 months, respectively. TRACP-5b, NTX and BAP were above normal levels at baseline in 62.5, 25 and 35.3 % of patients, respectively, and nearly 80 % of these patients attained normal levels during the treatment.

Although bone-modifying agents reduced the baseline levels of TRACP-5b, NTX and BAP significantly, the reduction patterns differed. TRACP-5b appears to affect levels most quickly and sensitively, possibly due to its direct link to the number and activity of osteoclasts. These findings suggest that the efficacy of TRACP-5b is clinically significant when considering which bone-modifying agents to use for breast cancer patients with bone metastases.