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Advances in Colorectal Cancer

New drugs show promise, but more research needs to be done.

Antiangiogenesis, at Last? continued...

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."

Shrinking Tumors

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.

Like Avastin, Erbitux is a monoclonal antibody. It also blocks the effects of a growth factor, although a different one called epidermal growth factor (EGF), which encourages the development of cancer cells. Unlike traditional chemotherapy, in which toxic drugs don't discriminate between the tumor and healthy cells, Erbitux and Avastin are targeted and cause fewer side effects.

It's important to understand that Erbitux did not lengthen the lives of the people in the study. So the results may seem like modest success at best, and you may wonder at the benefit of shrinking a tumor if it doesn't help someone live longer.

But Mooney points out that this wasn't the trial's purpose.

"The results may seem disappointing, but the study wasn't designed to see if [Erbitux] helps people live longer," she says. Instead, the purpose was to see if the drug worked well enough to merit further trials, which it did.

According to Mooney and Chen, further trials are now under way testing the full potential benefits of the drug. As with the current Avastin trials, the next step is to try Erbitux in people with less advanced colorectal cancer and in combination with other medications.

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