Clinical utility of serum osteocalcin

Prostate-specific antigen and other markers of therapeutic response

Several new agents and combinations demonstrate significant activity in the treatment of patients with hormone refractory prostate cancer. Prostate-specific antigen (PSA) is being used increasingly as the key marker of a therapeutic response in trials of new agents. This article reviews data that support this marker as a surrogate endpoint, and it discusses the issues around the appropriateness of PSA as an intermediate marker with evolving noncytotoxic agents. Other biomarkers of prostate cancer progression are not uniformly elevated in men with advanced disease; to date, they are of limited clinical use. This article also discusses the rationale and results of novel and alternative biomarkers of prostate cancer progression.

Serum bone alkaline phosphatase and CA 549 in breast cancer with bone metastases

A monoclonal radioimmunometric assay for bone alkaline phosphatase (BAP) developed by Hybritech, USA, with an upper limit of normal of 40 U/l, was examined in 125 patients with breast cancer. Eleven patients who remained tumour free for 5-6 years had small intra-individual variations of BAP. The median value in 33 patients with multiple bone metastases of 60 U/l was elevated when compared with that in 40 patients with no evidence of metastases (22 U/l) and 34 U/l in 16 with limited bone disease (1-2 hot spots). By contrast, only 2 out of 25 patients with extensive local recurrence, lung, or hepatic metastases, without bone involvement showed an increase of BAP (< 200 U/l). The BAP levels were compared to total alkaline phosphatase (TAP), the breast cancer marker CA 549 (HybriBREScan). Longitudinal studies of 15 patients with bony metastases showed that TAP and BAP were well correlated only when the TAP was elevated; CA 549 and BAP could vary independently. The main use of BAP in patients with bone metastases appears to be an aid to the monitoring of treatment; however, it is not significantly raised in limited bone metastases.

Osteocalcin: diagnostic methods and clinical applications

Osteocalcin is a small (Mr 5800), very interesting bone specific protein, synthesized by osteoblasts and measured in plasma as a biochemical indicator of bone formation. Many immunoassays for osteocalcin have been developed, including radio- and enzymoimmunoassays, with the use of monoclonal and polyclonal antibodies. These are used in many different clinical settings, including bone, kidney, and liver diseases. However, there is a wide range of published values for plasma osteocalcin concentrations in control and patient samples and this has hindered a more widespread adoption of osteocalcin measurement by clinicians. This review discusses how various immunoassays for osteocalcin may contribute to the wide variation of published values and suggests approaches for the development of standardized assays. For example, epitope specificity and immunoreactivity with multiple forms of osteocalcin and osteocalcin peptides in plasma are discussed. It also includes a recent update on interesting clinical applications of osteocalcin.