Advances in Colorectal Cancer
New drugs show promise, but more research needs to be done.
Antiangiogenesis, at Last? continued...
Avastin is the first of a long-awaited and new kind of cancer treatment, so-called angiogenesis inhibitors, which starve tumors by blocking blood vessel formation in them.
For many cancer researchers, antiangiogenesis has been the Holy Grail of drug development. Cancer cells need blood flow to grow, and the formation of new blood vessels is called angiogenesis. For decades, researchers have been working on a way to prevent the formation of new blood vessels.
Avastin is a monoclonal antibody, which is a manufactured version of the natural antibodies that the body uses to defend itself against foreign substances. It's designed to block the effects of the vascular endothelial growth factor (VEGF), a substance in the blood that helps these tumors grow new blood vessels.
Because of its specific target, Avastin also has few side effects, especially when compared with the toxic effects of traditional chemotherapy.
Researchers still have a lot to learn about the drug. The recent trial of Avastin was only in people with advanced colorectal cancer that had spread elsewhere in the body. The next step is to use Avastin in people with earlier stages of the disease, where the chances of curing it should be higher. Researchers are conducting trials now, Mooney says.
While the success of an angiogenesis inhibitor is exciting, Avastin has not been successful in treating other kinds of cancer.
"We know from an unsuccessful breast cancer trial that Avastin is not a magic bullet," says Helen Chen, MD, senior investigator in the Investigational Drug Branch at the National Cancer Institute. "At this time, it's hard to predict which patients with which cancer will benefit most. It's important to wait for the clinical trials to come out before we use Avastin in practice."
Erbitux, a new drug recently approved by the FDA for metastatic colorectal cancer, has also made news. When used in combination with the chemotherapy drug Camptosar, a study showed that Erbitux shrank the tumors in 23% of the people who had metastatic colorectal cancer and had exhausted other chemotherapy treatment options; it also slowed the tumor's growth by about four months. On its own, Erbitux shrank tumors by 11% and delayed the growth of the tumor by one-and-a-half months.