FDA Gives Conditional OK to Avastin for Breast Cancer

But despite this, the study found that the women on Avastin didn't live significantly longer than those on Taxol, and they experienced more adverse side effects, such as high blood pressure, blood clots and bowel perforation. Moreover, six deaths were linked to Avastin's toxicity.

A Last Hope for Some

While the drug has not yet been proved to extend the lives of women battling breast cancer, some experts say the approval of Avastin is justified solely on the basis that it could improve the quality of life of those with the disease.

In that respect, Avastin would not be the first drug whose approval was pegged to the possibility that it could lead to an easier life for cancer patients, rather than a longer one. Last March, the FDA decided to approve another breast cancer drug, called Tykerb, for similar reasons.

"As we move forward with targeted therapies, we're going to run into this situation more and more frequently," Lichtenfeld said. "So if we start thinking in terms of converting cancer from a fatal disease to a chronic disease ... drugs that improve quality of life will become more important."

Breast cancer is a curable disease, but once it has metastasized it is considered treatable but not curable. The American Cancer Society estimates that 40,000 women die of metastatic breast cancer each year. Of those, Genentech estimates that 38,000 have tumors that might respond to Avastin.

"Athough metastatic breast cancer remains incurable despite drugs like Herceptin, Avastin and others, it is eminently treatable," said Dr. Joseph Sparano, associate chairman of the department of oncology at the Montefiore Medical Center in New York. "In my view, a drug that doubles the chance of controlling the disease but doesn't affect survival is just as useful as one that prolongs survival by a few months."

Genentech estimates that 75 percent of women found to have breast cancer that has already spread have tumors that are HER2-negative -- and thus may be helped by Avastin.