Deconstructing Avastin

A mounting body of safety data led to Genentech Inc.'s recent decision to issue a "dear healthcare provider" letter warning that certain patients taking Avastin bevacizumab are at increased risk of arterial thromboembolic events. Now that the company has been able to identify specific risk factors, the next task is to figure out exactly why the monoclonal antibody causes the side effect, and whether there is a class effect.

Avastin, the first inhibitor of vascular endothelial growth factor (VEGF) to reach the market, was approved in March to treat metastatic colorectal cancer...