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Old 05-19-2005, 08:16 PM   #1
Rich
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http://www.forbes.com/technology/sciences/...0519tumors.html




Pharmaceuticals
When Shrinking Tumors Isn't Enough
Matthew Herper, 05.19.05, 6:00 AM ET

After working on a clinical trial that proved that a new Pfizer drug extends the lives of patients with stomach cancer, George Demetri, an oncologist at the Dana-Farber Cancer Center, tried a question out on his wife: If a new cancer drug is shrinking tumors, should that be enough to get it approved?

Demetri's wife, who is also a doctor, told him that she didn't see why shrinking tumors wasn't in itself a good thing. That idea fits neatly with common sense, but researchers increasingly say that it may not be true.

"I don't think the public as a whole understands that at all," says Demetri. "What if you shrink the tumor and the fatal event comes at the same time as it would have otherwise?"

When a new cancer drug is first tested in humans, cancer doctors look to see if it shrinks tumors. After all, cancer growths don't tend to shrink rapidly on their own, so a drug that shrinks tumors must be doing something.

But now doctors are finding that tumor shrinkage, on its own, isn't necessarily a good reason to use a drug, because it's entirely possible to shrink a tumor without helping the patient. More important measures of efficacy are how long it takes for the cancer to start worsening and how long patients live. If a drug increases survival time, its efficacy clearly outweighs any side effects.

Doctors still think of the number of tumors shrunk by 30% or more--technically known as the response rate--as an important indicator. But it is less than clear what it measures. "We've learned that response rate might be a poor measure of benefit," says Susan Desmond-Hellmann, who heads up clinical trials at Genentech (nyse: DNA - news - people ).

Kathy Miller, a breast cancer expert at Indiana University who has worked on trials of Sutent and Genentech's Avastin, says that her patients are very good at understanding that if a drug is keeping their tumors from growing, that is often good enough. But their families sometimes have more trouble. "My patients want to live better and longer," she says. "Response is a very poor surrogate for those more important goals."

Other experts say that, even for doctors, response rates can be compelling.

One place where this may play out is in a likely battle for market share in kidney cancer between Sutent and Sorafenib, a drug developed by biotech Onyx (nasdaq: ONXX - news - people ) and drug giant Bayer (nyse: BAY - news - people ). Onyx has data showing that Sorafenib slows tumor growth, compared with a placebo, but in late-stage trials only 2% of patients had their tumors shrink enough to be counted in the response rate. In a midstage trial, Sutent had a 40% response rate.

That high number could wind up being lower in later trials. But since the two drugs work similarly and may hit the market at about the same time, many doctors and analysts say the Pfizer medicine may have the upper hand, because it will be seen as more effective.

But the issue has come up before. One of the big problems in getting approval for Erbitux, the cancer drug developed by ImClone (nasdaq: IMCL - news - people ) and Bristol-Myers Squibb (nyse: BMY - news - people ), was that it only had data showing it shrank tumors, not that it helped patients. Even now, says Nicholas Vogelzang, director of the Nevada Cancer Institute, there is a real "paucity" of data for Erbitux, compared with that available for other targeted agents, such as Avastin.

However, Demetri says that focusing on harder evidence, like survival data, does not have to mean it will take longer for drugs to be developed. In the form of cancer he studies, genetic information has meant that drugs can be developed very rapidly. It took just three years to prove that Sutent benefited his patients. "Instead of massive studies to show a little effect," he says, "we'd like smaller studies to show a big effect."


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