All cancers, including colorectal cancer, require the growth of new blood vessels, called angiogenesis, to grow beyond a few millimeters in size. Like healthy tissues, these blood vessels supply the tumor with critical oxygen and nutrients. A major treatment advance in recent years has been the development of drugs, called angiogenesis inhibitors, that interfere with the tumor blood supply.

In 2004, the U.S. Food and Drug Administration (FDA) approved the first specifically designed angiogenesis inhibitor, bevacizumab (Avastin^®), to treat advanced CRC. Bevacizumab is an antibody therapy—a type of intravenous drug that binds to and neutralizes specific proteins. Cancerous tumors produce so-called angiogenic proteins, known as growth factors, to stimulate the growth of new blood vessels. Bevacizumab targets the most critical and best-studied angiogenenic protein, vascular endothelial growth factor (VEGF).

Another critical growth factor in CRC is epidermal growth factor. This protein binds to a receptor, called the epidermal growth factor receptor (EGFR), on the surface of tumor cells, much like a key fits into a lock. EGFR contributes to a number of processes involved in CRC development and progression, including angiogenesis. About 80% of malignant tumors of the colon and rectum “express” EGFR.

Two antibody therapies, cetuximab (Erbitux^®) and panitumumab (Vectibix^®), are used to treat patients with CRC that has become resistant to other treatment. While not expressly antiangiogenic, cetuximab and panitumumab indirectly interfere with VEGF production by tumor cells among other activities. In addition to disrupting the tumor blood supply, antiangiogenic drugs may also make chemotherapy and radiation treatments more effective.