The US Food and Drug Administration has approved Avastin (bevacizumab) to treat colorectal cancer that has spread to other parts of the body. The drug has been shown to prolong life by about 5 months when given in combination with standard chemotherapy drugs.

"Avastin represents an exciting breakthrough," said Len Lichtenfeld, MD, deputy chief medical officer for the American Cancer Society. "It is especially significant since colorectal cancer has been so difficult to treat with more standard chemotherapy treatments."

Colorectal cancer is the third most common cancer in both men and women in the United States, and is expected to kill nearly 57,000 people in 2004. Screening tests can prevent this cancer entirely, or find it at its earliest stages, when it is highly treatable. However, only 38% of colorectal cancers are discovered early. More often, the cancer is not found until it has spread and is difficult to treat.

Avastin, manufactured by Genentech, is a monoclonal antibody that works by preventing angiogenesis, the formation of new blood vessels in the tumor. This strategy starves the tumor of oxygen and other nutrients it needs to grow. Researchers have been working on drugs to attack cancer in this way, but Avastin is the first successful one.

The FDA based its approval of the drug primarily on a trial of more than 800 patients with advanced colorectal cancer. Half the patients received the standard chemotherapy treatment with irinotecan, 5-fluorouracil, and leucovorin (the Saltz regimen). The other half got the standard treatment plus Avastin. Patients who got Avastin lived an average of about 5 months longer, and it took about 4 months longer for the tumors to begin growing again.

Avastin can have some serious side effects, including the formation of holes in the colon that may need to be treated with surgery. Lichtenfeld said it is not clear whether this side effect is a toxic effect of the drug or a result of the tumors simply shrinking and leaving empty space in their place. More common potential side effects are high blood pressure, fatigue, and blood clots.

Avastin is the second high-profile drug approved for colorectal cancer in recent weeks. The FDA also approved Erbitux, manufactured by ImClone Systems, for patients with advanced cancer who are no longer responding to irinotecan or who cannot take that drug. Unlike Erbitux, however, Avastin is approved as a primary treatment.

"That, and the fact that the results of the Avastin trial were so clear-cut, make it likely that this drug will be adopted quickly into standard treatment regimens for metastatic colorectal cancer," Lichtenfeld said.

Avastin is also being tested for use against other cancers.

"Our knowledge about the effectiveness of this drug will develop only as quickly as patients, their families, and their physicians, are willing to refer and participate in well-designed clinical trials," Lichtenfeld noted.