Invasion and metastasis: biology and clinical potential.

Metastatic dissemination of tumor is the primary cause of death for most cancer patients. The expanding field of study of the metastatic cascade has been the source of novel approaches to the diagnosis and treatment of cancer. The metastatic process involves angiogenesis, tumor cell adhesion to vascular basement membrane, local proteolysis to create an opening in the basement membrane, migration through that rent and into the secondary site, and finally, successful proliferation. Important components of the metastatic cascade such as basement membrane structures, adhesion molecules and their receptors, proteolytic enzymes, migration-inducing factors, and growth factors have been demonstrated to have reproducible patterns in malignant and metastatic tissues. These patterns have led to clinical correlations demonstrating their utility in the identification and follow-up of malignant and metastatic disease. In addition, several promising new anti-cancer drugs such as inhibitors of angiogenesis, protease-inhibitors, and blockers of signal transduction have been identified and are awaiting introduction into the clinical arena.