Because Genentech is a leading developer of cancer therapies, some doctors also fear that the company's pricing plans for Avastin -- around $8,800 a month -- may encourage other companies to charge more for their own oncology drugs. That could potentially drive up the overall cost of cancer treatment to unsustainable levels, they say.

Right now, one of the few cancer drugs with a higher monthly price than the level planned for Avastin is Erbitux. The drug, used for colon cancer, sells for $9,600 monthly, but is not as widely prescribed as Avastin and is typically used only as a last-resort treatment for a few months.

Dr. Susan Desmond-Hellmann, the president of product development of Genentech, which is based in South San Francisco, Calif., said that Genentech had set Avastin's price based on "the value of innovation, and the value of new therapies." Genentech, which had more than $6 billion in sales last year, has many programs to help patients afford its medicines, and last year contributed $21 million to charities that help patients with their insurance co-payments, she said.

Genentech intends to file an application later this year with the Food and Drug Administration to expand the drug's label to include treatment for breast and lung cancer. While nothing stops doctors now from prescribing Avastin for those diseases, F.D.A. approval would let the company promote and advertise it for such treatments and make insurers more likely to pay for the treatments.

For now, insurers are deciding case by case whether to cover Avastin for breast and lung cancer, and in many instances they are rejecting coverage or at least delaying decisions.

"Insurers may say, 'It's not approved for that indication, so we're not paying for it,' " said Dr. Paul A. Bunn Jr., the director of the University of Colorado cancer center.

In those cases, patients must sign a waiver agreeing to reimburse the hospital for the price of treatment if the insurer will not agree to do so. And some patients are afraid to sign the waivers, Dr. Bunn said. "A couple of patients have refused to sign or take treatment."