Comparison of Assay of Total and Bone-Specific Alkaline Phosphatase in the Assessment of Osteoblast Activity in Patients with Metastatic Bone Disease
The evaluation of response of osseous metastases to systemic treatments is often low as a consequence of the different radiologic appearances that make objective assessment not only difficult but sometimes impossible. Radiographic evidence of recalcification, the UICC criterion of response, is often evident for 6 months and sometimes may be delayed even more. This accounts for lower response rates in bone with respect to other metastatic sites in clinical trials. A transient rise in bone formation indices may provide an early indication of bone healing and, along with measurement of symptomatic changes, could ameliorate the response evaluation. Among the biochemical markers of bone formation, total alkaline phosphatase (TALP) is widely employed, but it lacks specificity. Estimation of bone isoenzyme (E-BALP) by electrophoretic techniques is time consuming and semiquantitative. The immunoradiometric assay (I-BALP) seems to overcome these limitations. In this study, we compared the two methods of bone isoenzyme estimation with each other and with the levels of bone gla protein (BGP) and carboxyterminal propeptide of type I procollagen (PICP) in a group of 136 cancer patients with bone metastases stratified as having lytic or mixed and blastic lesions at X-ray, and in 62 cancer patients without apparent bone involvement. The same indices were also evaluated prospectively in a patient subset submitted to chemotherapy associated with pamidronate. The aims of the study were to evaluate whether I-BALP is superior to E-BALP and whether both methods of bone isoenzyme estimation are more advantageous than TALP, BGP, and PICP in the assessment of osteoblast activity either in baseline conditions or in response to treatment. In bone metastatic patients with lytic appearances, values above the cut-off limit were observed in 32.1%, 23.3%, 48.9%, 32.9%, and 14% for, TALP, E-BALP, I-BALP, PICP, and BGP, while the corresponding percentages in those with blastic/mixed appearances were 74.0%, 84.8%, 76.9%, 51.9%, and 43.8%, respectively. In the patients without bone involvement, values within the normal range were 90.2%, 98.2%, 89.6%, 71.7%, and 90.2%, respectively. Levels of TALP, E-BALP, and I-BALP were reciprocally correlated in the three groups examined. In bone metastatic patients, however, the degree of correlation of the enzymes with PICP and BGP was weak. Liver isoenzyme of alkaline phosphatase (LALP) was found to correlate with E-BALP, but not with I-BALP, in patients with mixed/blastic lesions. Thirty-eight patients were submitted to pamidronate therapy (60 mg every 3 weeks, administered 4 times) in association with cytotoxic treatment. Osteoblastic markers were determined before any administration. Serum TALP, E-BALP, and I-BALP showed a transient rise in 9 cases, a progressive reduction in 12, no change in 2, and a progressive increase in 6. Changes in E-BALP and I-BALP from baseline were greater than those of TALP. A divergent pattern between TALP and both I-BALP and E-BALP was found in 9 patients, whereas a divergent temporal profile between the two methods of bone isoenzyme estimation was recorded in only 3 patients. Eight out of 38 cases obtained a partial recalcification of lytic and mixed lesions. Seven of them showed the concomitant early increase in TALP, E-BALP, and I-BALP followed by a gradual decline (osteoblastic flare), whereas 1 patient demonstrated the flare of E-BALP and I-BALP but not of TALP. No relationship was found between response and temporal changes in in BGP and PICP serum levels. We conclude that I-BALP is a useful marker for detecting excess osteoblastic activity in patients who have at imaging ``pure'' lytic bone metastases. In the longitudinal evaluation of patients receiving multiple pamidronate infusions plus chemotherapy, TALP, E-BALP, and I-BALP, but not BGP and PICP, appeared to be useful to identify responders in bone. A slight advantage of measurements of serum bone isoenzyme (by both techniques) over TALP is apparent, but this study fails to demonstrate a clear superiority of I-BALP over E-BALP.