Osteocalcin: is it a useful marker of bone metastasis and response to treatment in advanced prostate cancer?

Serum osteocalcin (OC) is derived largely from new cellular synthesis. It is a marker for bone formation and a noninvasive specific marker of osteoblastic activity. The clinical significance of OC in monitoring prostatic cancer bone metastases was evaluated. Pretreatment serum OC levels were determined with a radioimmunoassay kit in a total of 63 patients with prostate cancer (8 with stage B, 12 with stage C, 12 with stage D1, and 31 with metastatic bone disease). The OC levels in patients with skeletal metastasis were significantly higher than those in patients without bony lesions (P less than 0.01). The pattern of the initial changes in OC levels were analyzed in patients with skeletal metastasis who received endocrine treatment. The pretreatment OC value is of little use in predicting the response to treatment. The patients whose OC level initially increased and remained high tended to have a shorter interval to disease progression. On the other hand, the pattern of initial changes in OC varied according to the regimen of endocrine treatment. Our study suggests that OC seem to reflect the response to treatment and might lead to the improvement in follow-up procedures. However, the clinical significance of OC as a marker of the response of bone metastasis should be carefully discussed with regard to the direct hormonal effect on bone metabolism.