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
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.