A panel of federal advisers Wednesday voted to proceed with the government’s plans to revoke the approval of the drug Avastin for women with advanced breast cancer.

The Food and Drug Administration’s six-member Oncologic Drugs Advisory Committee voted unanimously against reversing a decision to pull Avastin’s approval for breast cancer, concluding that research had failed to show the drug significantly extended patients’ lives or improved the quality of their lives and was worth exposing patients to its potentially life-threatening side effects.

The conclusions came in a series of votes that the committee took at the end of an unusual two-day hearing convened to determine the fate of the drug’s approval for breast cancer treatment.

The closely watched vote marks a blow to the drug’s maker, Genentech, as well as breast cancer patients and advocates who had pleaded with the agency to reverse its decision.

The committee rejected a request by Genentech that the approval be left in place while the company conducted another study to try to prove the drug’s usefulness.

FDA Commissioner Margaret A. Hamburg will use the committee’s recommendations to decide whether to proceed with the withdrawal of its approval. FDA commissioners are not required to follow the guidance of their advisory committees, but usually do.

The decision about Avastin, which is among the most expensive medications, is being closely watched by patients, oncologists, women’s health advocates, health-care policymakers, economists and the pharmaceutical industry. The FDA has stressed that the price is irrelevant. But critics have charged the revocation was evidence of the government’s move toward rationing health care. The case has also become a rallying point for advocates for patients suffering from other diseases concerned about restricting access to promising new treatments.

But the withdrawal has been supported by others, including several leading breast cancer advocacy groups and experts who said it was important for the agency to base its decisions on the scientific evidence, not emotional appeals, especially when lives are at stake and controlling health care costs is so crucial to the nation’s economy.

Until Hamburg’s final decision, Avastin is still approved for breast cancer. If the drug is revoked for that treatment, it would remain available to treat cancer of the brain, colon, kidney and lung. Doctors could continue to prescribe it for breast cancer as an “off-label” use.

But the loss of FDA approval of Avastin for breast cancer would likely prompt insurance companies to stop paying for the drug for that use. Breast cancer patients also would lose eligibility for a Genentech patient assistance program that caps the annual cost of the drug at about $57,000 for women making less than $100,000 a year.

The trial-like advisory panel meeting, the first time the agency has convened a hearing on a drug company’s appeal of such a decision, was marked by unusually tense exchanges between company and agency representatives. The officials clashed repeatedly over a variety of issues, including the interpretation of the data about the drug’s effectiveness, and whether the agency had shifted its criteria for approving the drug.

In a series of presentations, scientists from Genentech Wednesday argued that the agency had approved other drugs based on similar evidence of safety and effectiveness and noted that other regulatory bodies, including the European Medicines Agency, have accepted the existing data for Avastin. The firm asked the agency to retain the drug’s authorization while the company conducts another study to clearly demonstrate its benefits.

“What we cannot lose sight of is the many women behind these numbers,” said Hal Barron, chief medical officer, at the conclusion of the company’s presentations. “These women have a significant unmet need.”

About 30 or 40 protesters, many wearing pink T-shirts and carrying signs reading “Save Avastin” and “I question the FDA’s right to take life from a woman” demonstrated outside the agency’s Silver Spring headquarters as the hearing began Tuesday. And members of the public presented arguments — including often-emotional pleas from patients, family members and advocates — to keep the drug available for breast cancer treatment.

But the panel also heard from some advocates who argued that more women were being harmed than helped by the drug. And after the public comments, FDA officials gave a series of detailed scientific presentations to bolster their argument that the existing data indicated that Avastin provided little or no benefit and put women at risk for potentially life-threatening complications.

Avastin was the first drug designed to fight cancer using a new strategy — inhibiting blood flow to tumors. But its 2008 approval for breast cancer was controversial from the start. Only one study had found that the drug appeared to slow the growth of an advanced breast tumor, delaying progression by about five months. It remained unclear whether patients lived longer or enjoyed any better quality of life. So the FDA authorized Avastin under a special program designed to make advances in treatment available to patients quickly. The deal is that pharmaceutical companies must immediately validate the risk-benefit ratio of such drugs.

The FDA announced in December that it was pulling the approval after concluding that Avastin does not help patients with metastatic breast cancer live longer or help them in other ways worth risking its potentially life-threatening side effects. The decision came after a July 20, 2010 advisory committee concluded that the new studies had not shown that the drug extends life and indicated that the drug slowed tumor growth for only perhaps as little as a month. At the same time, Avastin can cause very high blood pressure, hemorrhages, heart attacks and heart failure.

Avastin is one of the costliest of a new generation of anti-cancer medications that appear to give patients perhaps a few extra months of life. Genentech, which has waged an unprecedented campaign to save the drug’s U.S. approval, gets about $8,000 a month for Avastin for breast cancer treatment. Before the FDA announced plans to withdraw the approval, Avastin was being prescribed to about 17,500 breast cancer patients a year in the United States, bringing in nearly $1 billion annually. Globally, Avastin had annual sales of $6.8 billion in 2010, making it the top-selling product for Genentech and its parent company, Roche, and the world’s top-selling cancer drug.