Genentech's Avastin cancer drug should be rejected for the use in the United States, advisers said on Wednesday.

A U.S advisory panel of cancer drug experts rejected a bid by Genentech to win approval for the drug designed to treat women with advanced breast cancer. The panel voted 5-4 that the drug's benefit in slowing tumor growth isn't worth the added risk of serious side effects, including high blood pressure and death.

Genentech's shares traded down nearly 10 percent at a two-and-a-half-year low after the panel vote. The stock was halted shortly after the news.

Avastin represents Genentech's second most popular drug, with sales reaching $2.65 billion in the first nine months of this year. It is approved for treating lung and colon cancer.

If approved for breast cancer that has spread to other parts of the body, Avastin could add $1.3 billion in 2009, analysts say.

The FDA typically follows the recommendations of its advisory committees, though it is not required to do so. It is expected to make an official decision by Feb. 23.

Shares of Genentech fell 6.6, or 9 percent, to $66.18 before trading in the stock was halted at 2:29 p.m.