Antiangiogenics and metastatic colorectal cancer: Who is an optimal candidate?

Angiogenesis is a tightly regulated process that is mediated by a group of angiogenic factors such as vascular endothelial growth factor and its receptors. Given the widespread use of antiangiogenic agents, there has been considerable interest in developing methods to identify subgroups of patients who would preferentially benefit from those treatments. The overlap between the various angiogenic factors, vascular endothelial growth factor, and its multiple isoforms or splice variants presents a significant challenge to assessing the consequences of activation or inhibition of the angiogenesis pathway and thus represent a challenge to biomarker discovery. Multiple biomarkers are in various phases of development and include tissue and serum biomarkers, as well as novel imaging techniques. Patient selection for angiogenesis inhibitors, however, continues to depend mostly on risk-factor assessment as it relates to their anticipated side-effect profile. In this review we discuss the state of biomarker discovery for agents that target the angiogenesis pathway, with a main focus on currently approved therapies.