WASHINGTON -- A drug made by Genentech received federal approval on Friday to treat breast cancer, a decision that could represent a major shift in standards for assessing the effectiveness of cancer medicines.

Going against the recommendation of its advisory panel, the Food and Drug Administration cleared Genentech's Avastin, which is already approved for treating lung and colon cancer, based on findings that it slowed tumor growth.

Advocates for breast cancer patients applauded the ruling.

Genentech said FDA granted the drug preliminary approval and the company will have to submit additional data.

FDA approval for late-stage cancer treatments is usually contingent upon data showing a drug extended, or improved the quality of, patients' lives. Avastin showed neither in a study, according to Genentech's application.

Instead Genentech showed that the drug slowed tumor growth, without actually increasing life expectancy. Cancer experts have long debated whether that measure is as significant as survival rates for measuring a drug's effectiveness.

Wall Street analysts believe FDA's Avastin decision opens the door for other cancer drugs to be approved for their tumor-shrinking capabilities — a trend that worries some health experts.

"If FDA sets a precedent of approving a drug based on progression free survival, people are afraid they may stop looking at survival as the most important endpoint," said Dr. Kay Dickersin, director of the Center for Clinical Trials at Johns Hopkins University.

The questions surrounding Avastin's effectiveness have caused debate among cancer experts, doctors and patients.

In December, a panel of outside FDA advisers voted 5 to 4 against Genentech's application, indicating the drug's benefits did not outweigh toxic side effects.

Despite the panel's narrow recommendation against the drug, many U.S. doctors continued prescribing it "off-label," or without a federal endorsement, for breast cancer. Genentech has previously estimated that more than 9,000 breast cancer patients receive the drug this way.

Some insurers have been reluctant to pay for the injectable drug, which can cost $100,000 for a year's supply. Dr. Joseph Sparano said he prescribes Avastin because it has shown better results at slowing breast cancer growth than any other drug on the market.

The Y-Me National Breast Cancer Organization called Avastin an important new option for patients.

"The benefits we're looking at with Avastin matter because they give patients hope," said Margaret C. Kirk, the group's president. "Without disease progression they may survive to see a discovery that can help them in the future."