Lee M. Ellis, MD, FACS

In this issue of ONCOLOGY, Olszewski,Grossbard, and Kozuchprovide an excellent overview ofthe role of antiangiogenic therapy inthe treatment of patients with metastaticcolorectal cancer. The authorshave brought several important issuesto the forefront that warrant furtherdiscussion, and these issues will beaddressed in this commentary.

The treatment of colorectal cancer has undergone enormous changesin the past decade. From a disease with a single treatment option (ie,fluorouracil, a modestly effective drug), the treatment options haveevolved to include at least five new classes of antineoplastic agents.Among the considerable number of recently approved drugs, two aremonoclonal antibodies and are the testing ground for our rapidly emergingknowledge about cancer cell biology. Cetuximab (Erbitux) targetsthe epidermal growth factor receptor, an important molecule involvedwith cell cycling, survival, invasion, and metastasis. Bevacizumab(Avastin) neutralizes the vascular endothelial growth factor, blockingits ability to activate its receptor on the endothelial cells. The developmentof both antibodies resulted from decades of research in molecularand cell biology, as well as preclinical and clinical studies, and signalsa new paradigm where the tumor cells’ own unique features areexploited in a rational way.

Angiogenesis is a dynamic process essential for primary tumor growth and metastases. New insights into the basic understanding of the biologic processes responsible for angiogenesis have led to the characterization of potential therapeutic targets. Several strategies for the development of antiangiogenic therapeutic modalities have been employed, including agents that (1) decrease the activity of specific angiogenic factors, (2) decrease the activity of endothelial survival factors, (3) increase the activity of naturally occurring antiangiogenic agents, or (4) indirectly downregulate angiogenic and survival factor activity.

Tumor angiogenesis is a complicated process that is regulated by numerous factors simultaneously and in a coordinated fashion.

Angiogenesis is essential for the growth of both primary andmetastatic tumors. This process, more complex than was previously thought,