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MICHELE NORRIS, host:

There's been progress in preventing death from lung cancer in heavy smokers. That's according to a study of more than 50,000 people. It shows that a CT scan can pick up lung cancers at an early stage, and cut the rate of death by 20 percent. This is a surprising result for a test that has generated a lot of controversy, and NPR health correspondent Richard Knox joins us now.

Richard, first of all, tell us more about the new study.

RICHARD KNOX: Well, first of all, it's the biggest lung-cancer screening study ever done, with 53,000 men and women over age 55. They all had a heavy smoking history - meaning they smoked the equivalent of a pack a day for 30 years.

It cost around a quarter of a billion dollars. And it's also the only study that so far, has met the gold standard for scientific studies, which means that it randomly assigned people to get either CT screens of their lungs, or regular chest X-rays. Other studies didn't have this random comparison group. Or other studies had other problems that didn't really allow anybody to conclude that the CT screening really made the difference.

The new study shows very clearly, I think - and most people I've talked to today say persuasively - that CT screening does work to reduce death from lung cancer. As you said, it reduces the risk by about 20 percent.

And by comparison, mammography, regular mammograms may reduce the risk of death from breast cancer by about 30 percent. There's controversy over that, too, of course. But it's in the same ballpark.

NORRIS: And does it reduce the risk because of early intervention, catching this in an early stage?

KNOX: That's the best hypothesis. I mean, it's a very complicated question. But Dr. Harold Varmus today - who's the director of the National Cancer Institute - said that's the best explanation, that CT screening of the lungs does detect little, tiny cancers that don't cause symptoms. And by catching them early, they are more treatable and more curable.

NORRIS: What's all the controversy been about?

KNOX: Well, it's been largely about whether CT screening really does reduce deaths. Earlier studies just couldn't say, for reasons that I mentioned. They didn't have this kind of rigorous design.

Also, there's been a lot of controversy about the downsides, which mean like, things - false alarms, things that are discovered that really aren't cancer, and the dollar cost and the psychic cost of the additional tests that are necessary to rule out cancer. And inside science, there's been a lot of controversy about the quality of the evidence that we would need in order to go down this road - because it's going to be a big undertaking to implement screening on a wide basis.

NORRIS: Quick question before I let you go - two, actually: Is the National Cancer Institute recommending that all smokers get a CT scan? And how expensive is this, and does insurance pay for it?

KNOX: No, the National Cancer Institute is not recommending everybody -all smokers get CT scans, or is not saying anything so far about how often anybody should. That's going to be threshed out over the months to come, by a lot of different groups.

It costs about $300 a test and no, insurance generally doesn't pay for it yet.

NORRIS: Thank you, Dick.

KNOX: Any time.

NORRIS: That was NPR health correspondent Richard Knox.

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