Why do tumors metastasize?

Approximately 90% of all cancer deaths can be attributed to the metastatic spread of primary tumors. An understanding of the process by which cells from a localized tumor invade adjacent tissues and migrate to distant organs is crucial for the development of anticancer strategies that can efficiently prevent this process. Although our knowledge of cancer has increased in recent years, the molecular mechanisms of tumor invasion and metastasis still remain elusive. This report discusses recent data that suggest that tumors metastasize because tumor cells have an alteration in oxygen metabolism (dysoxia). This alteration in oxygen metabolism would drive tumor invasion and metastasis via glycolysis-mediated extracellular acidification, excessive production of hydrogen peroxide (H(2)O(2)) and hypoxia-inducible factor 1 (HIF-1) activation. This new model might help develop cancer chemopreventive strategies for preventing tumor metastasis and thus reduce cancer mortality.