On Nov. 19, 2003, a novel approach to treatment of solid cancers involved therapeutic agents that inhibit the generation of new blood vessels in growing tumors (angiogenesis). The evidence linking tumor growth and metastases with angiogenesis is compelling: in colorectal and breast cancers, the density of microvessels in histologic specimens has been correlated with disease recurrence, metastases, and survival. Of the identified angiogenic factors, vascular endothelial growth factor has been shown to be the most potent and specific.