LOS ANGELES -- The cancer drug Avastin should not be used to treat breast cancer that has spread to other organs because it doesn't help patients enough to justify its risky side effects, the Food and Drug Administration ruled Friday.

The decision comes five months after an FDA advisory committee recommended that the federal agency withdraw its approval of Avastin for breast cancer patients. Clinical trial results have fueled doubts about its value for treating breast cancer for years.

Still, FDA Commissioner Margaret A. Hamburg said the choice was difficult because so many women and their doctors have put their faith in the drug and lobbied hard on its behalf.

"I did not come to this decision lightly," she said. "Sometimes, despite the hopes of investigators, patients, industry and even the FDA itself, the results of rigorous testing can be disappointing."

Avastin will remain on the market for treating other types of cancer where the benefits clearly outweigh the risks, such as lung, kidney and colon cancer, Hamburg said. As long as it's available, doctors will have the flexibility to prescribe it for breast cancer patients as an off-label use, though insurance companies may not be willing to pay for it.

The drug is a biological antibody designed to interfere with the blood supply that feeds a tumor and helps it grow and spread. But it can cause harsh side effects, including heart attacks and strokes.

The FDA approved Avastin for metastatic breast cancer in 2008 after a study in the New England Journal of Medicine showed that patients who took it in conjunction with a chemotherapy drug experienced six additional months of progression-free survival compared with patients who only took the chemo drug.

It was the first medicine to be OK'd under an accelerated approval program that allowed it to be used while researchers gathered additional data to clarify its safety and efficacy.