Surrogate biomarkers in evaluating response to anti-angiogenic agents: focus on sunitinib.

Conventional methods to assess the clinical activity of new agents that target specific biological pathways involved in tumour pathology may not provide correlation with clinically relevant outcomes such as patient survival or progression-free disease, and new and alternative methods should be explored. Biomarkers can assist in evaluation, and once validated, serve as a surrogate for clinical activity. Angiogenesis, a process well known to be involved in tumour growth and metastasis, is the target of several agents available today in the treatment of cancer. Laboratory assays used to detect proteins involved in angiogenesis and emerging imaging approaches have provided the bulk of the biomarker data to date in this area, and have already corroborated aspects of the biochemical basis of anti-angiogenic strategy. This symposium article will provide a brief overview of biomarker data in several different tumour types and discuss the effect that sunitinib and other anti-angiogenic agents have on these biomarkers. Surrogate biomarkers discussed include soluble proteins found in the blood or urine, circulating endothelial cells and their progenitors, and non-invasive imaging techniques.