Tumour invasion and metastasis: challenges facing drug discovery.

Initial attempts at directly targeting metastatic spread using inhibitors of matrix metalloproteases failed to deliver the promise of anti-invasive therapy. A new generation of targeted agents with the potential to act as anti-invasives has recently entered the clinic but there is, as yet, no clear route to demonstrate an effect upon tumour metastasis. Because advances with monoclonal antibodies are likely to increase the number of potential anti-invasive agents, more clinically predictive drug discovery cascades are required to reduce the perceived risks associated with their generation. Once they reach the clinic, new approaches will be essential to help early indicators of clinical response meet ethical standards and avoid unnecessary clinical failures.