Current concepts on pathogenesis and biology of metastatic osteosarcoma tumors.

Osteosarcoma (OS) remains the most common malignancy among orthopaedic neoplasms. Despite advanced surgical techniques and attempts to use second-line chemotherapy, 5 year overall survival in OS patients is still reported to be as low as 60-70%. Progression to metastatic disease is the main cause of treatment failures. Broadening current knowledge on the pathogenesis and biology of metastatic OS tumors is a key element in improving treatment results, i.e. identifying potential therapeutic targets. Recent studies have brought new concepts into this field. This paper outlines the most important issues which may influence treatment methods in the near future. In a few sections, we discuss (1) a model of OS dissemination with special regard to proteins mediating the lysis of the extracellular matrix; (2) the mechanisms protecting circulating OS cells from programmed death; (3) the relationship between angiogenesis, its pathogenesis, and OS metastatic potential; (4) the role of cytokines in OS progression and site-specific metastasis formation; (5) an example of treatment resistance mechanism - the P glycoprotein efflux pump; and, finally, we theorize on (6) whether cancer stem cells may play a role in OS progression.