Serum PICP as a bone formation marker in 89Sr and external beam radiotherapy of prostatic bony metastases

The clinical management of skeletal metastatic disease is problematic because of the difficulty in treating and accurately monitoring therapy impact and disease progression. This investigation measured serum procollagen type I C-terminal peptide (PICP) concentrations as a semi-quantitative index of bone turnover in patients with metastatic prostatic adenocarcinoma before and following palliative 89Sr chloride therapy. 10 patients with early stage (stage A2, B1 and B2) biopsy-confirmed prostatic adenocarcinoma were investigated (n = 10). Two groups of 10 patients each (n = 10 per group) with advanced (stage D) metastatic prostatic adenocarcinoma who had previously undergone hormonal manipulation were also investigated. One group of patients with scintigraphically documented metastatic bone disease received additional irradiation for new symptomatic bone metastases, whereas the other group received 89Sr chloride therapy. A radioimmunoassay for PICP was used to measure serum concentrations of patients in each of these groups as well as positive and negative controls. The concentration of serum PICP rose from 649 +/- 279 before treatment with external beam radiotherapy to 927 +/- 157 ng ml-1 4 months after therapy (p < 0.05). However, the results demonstrated a four-fold decrease (p < 0.001) in serum PICP in clinical responders to 89Sr chloride therapy versus baseline 4 months after the completion of treatment. The clinical non-responders demonstrated no significant change in PICP concentrations during that interval. This may be due to an increase in untreated bony metastases in the non-89Sr treated group. Although a relatively small representative group of patients was studied, these data demonstrate that serum PICP concentration correlates with clinical response to 89Sr chloride therapy. This objective laboratory technique may be useful for monitoring and predicting the need for 89Sr chloride therapy and optimizing palliative care. It may also be extremely useful in predicting a therapeutic response to such intervention.