Spiraling prices for new cancer therapies — up to $10,000 a month for a single drug — are causing alarm among patients and insurance companies.

"These costs are out of control," says Fran Visco, president of the National Breast Cancer Coalition, which is planning a conference focused on drug costs in the fall. "We can't allow it to continue."

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The cost of a cancer drug prescription rose nearly 16% last year, compared with 3% for other prescriptions, says a June report by Express Scripts, a pharmacy benefit manager. The average cost of a 30-day prescription for cancer drugs is now nearly $1,600. The report does not include drugs given at a doctor's office, such as Avastin.

Barbara Brenner of Breast Cancer Action says she is especially troubled by the cost of Avastin, a newer drug used to treat colorectal cancer that now sells for about $50,000 a year. That price could jump to $100,000 if Avastin is approved to treat breast and lung cancers, because those tumors are treated with higher doses of the medication.

"It's really exploiting the desperation of people with a life-threatening illness," says Marcia Angell, former editor of The New England Journal of Medicine.

In the past decade, researchers have been enthusiastic about Avastin and other "targeted" therapies, which are designed to attack tumors while causing fewer side effects than conventional drugs. These therapies may give patients a few more months, but they are not a cure. Given those limitations, Angell and others question whether the drugs are worth the price.

Tarsha Echols, 34, a flight attendant in Memphis, began taking Herceptin last year to keep her breast cancer from returning. That was before her employer cut her salary 35%. She plans to stop taking the drug Monday — a year early — because her health plan now requires her to pay 20% of her medical costs, or about $800 a month. That's more than her rent. "I hope that whatever I've gotten so far is enough," she says.

Rising cancer costs affect all Americans, says Sharon Levine of The Permanente Medical Group of Kaiser Permanente, the country's largest non-profit health maintenance organization. Taxpayers absorb much of the bill because most cancer patients are covered by government insurance such as Medicare.

Drug industry leaders say they try to make sure patients get the drugs they need. Companies gave away more than $8 billion in cash and products to poor or uninsured patients last year, according to the Pharmaceutical Research and Manufacturers of America.

Walter Moore, Genentech's vice president of government affairs, says profits help pay for research. "One can't be in business without returning a profit," he says. "To get the returns to be able to spend the money to do the things we want to do, we have to price the way we price."