A U.S. health panel begins meeting Tuesday to consider whether the world's best-selling cancer medicine, Roche Holding AG's Avastin, should retain approval for treating breast cancer.

Analysts say the Food and Drug Administration, which proposed removing the breast cancer indication in December, is unlikely to change its mind without new evidence about Avastin's ability to help breast cancer patients live longer.

For Swiss-based Roche, the FDA decision could shave almost a billion dollars off annual Avastin sales, according to analysts.

During the rare two-day appeals hearing, Genentech, a unit of Roche, is expected to argue the drug should be kept on the market pending new studies that show a more significant clinical benefit.

For patients, an FDA rejection of the appeal could mean insurance companies would stop covering the expensive drug for breast cancer, potentially jeopardizing treatment for an estimated 17,000 women currently using the medicine.

Some patient groups are expected to testify on Tuesday that Avastin should be kept on the market for breast cancer to give patients more treatment options. Breast cancer is the second-leading type of cancer among women after skin cancer.

The appeals panel will make a recommendation and the FDA will make the final decision.

LATER STUDIES LESS PROMISING
Avastin won U.S. clearance for breast cancer in 2008 based on a study showing the drug stalled cancer growth by 5.5 months. As part of an accelerated approval, the FDA required Roche to run follow-up studies to confirm the drug worked.

Later studies found only a one- to three-month delay in breast cancer growth. And no studies showed Avastin extended the lives of patients with advanced breast cancer.

Some patients also had severe side effects, including holes in the stomach and intestines, severe bleeding and blood clots. Roche says the rate of those side effects was low, less than 4 percent higher than standard chemotherapy.

In December, the FDA proposed revoking Avastin's clearance for breast cancer while keeping the drug on the market for colon, lung, brain and kidney cancers.

Genentech has been fighting the decision, saying the extension of time without cancer growing was meaningful for patients with advanced breast cancer. At that stage, the disease cannot be cured and the goal is to stabilize patients as much as possible.

Stripping the breast cancer indication for Avastin would not prevent doctors from using it. But without FDA approval, insurers may refuse to pay Avastin's $8,000-a-month price tag. And

Genentech would not be able to promote Avastin for that use.

UP TO $1 BILLION AT STAKE
Most analysts believe the panel will not change its mind, especially as five of the six members voted against Avastin's use in breast cancer at a hearing last July.

About $1 billion of Avastin's more than $6 billion in yearly sales come from breast cancer uses.

The product used to be Roche's top-selling drug, and some expected it to become the world's biggest-selling drug by 2014.

But its prospects have dimmed after doubts about its benefits in breast cancer and after it failed in clinical trials for prostate and stomach cancer.

Medicare, the U.S. federal health insurer, is likely to cut coverage for Avastin in breast cancer if the FDA revokes that use. That could shrink U.S. sales by half in 2011 to $400 million, said Karen Andersen, analyst at Morningstar.

But she sees a 60 percent chance that private health insurers would still keep coverage for Avastin on an off-label basis.