Clinical utility of biochemical marker of bone remodelling in patients with bone metastases of solid tumors

Bone turnover is characterized both by the formation of new bone by the ost eoblasts and the resorption of old tissue by the osteoclast. This process t akes place only on the surface of bone and can be described in terms of spa tio-temporal events that are the bone metabolic unit and the bone remodelli ng cycle. The former consists of a discrete group of cells (osteoblasts and osteoclasts) involved in a particular remodelling event while the latter r epresents the succession of resorption and formation. In a typical remodell ing cycle, resorption takes 7-10 days, whereas formation requires 2-3 month s. Remodelling is regulated either by local or systemic factors, including electrical and mechanical forces, hormones (e.g. parathyroid hormone, sexua l steroids, calcitriol, cortisol, thyroid hormone, calcitonin), growth fact ors and cytokines. Recently different circulating biochemical markers have been proposed for the investigation of bone turnover. In addition to classi cal parameters such as serum alkaline phosphatase and urinary calcium and h ydroxyproline, new markers have gained clinical attention because of their accuracy in assessing the dynamic changes in bone remodelling (bone alkalin e phosphatase, osteocalcin, propetides PICP and PINP tartrate-resistant aci d phosphatase, deoxypyridinoline, pyridinoline, telopeptide CTx and NTx). T he aim of this review is to present the recent advances in this field and t he clinical application of markers of bone turnover in patients with bone m etastases from solid tumors. Also the cellular and molecular bases of bone remodelling are reported with details.