That increased to 88 percent if the cancer was detected in an early stage, and to 92 percent if such patients had surgery within a month of diagnosis. The eight untreated patients all died within five years of diagnosis.

"When you find it when it's small, you can essentially cure most of them," Henschke said.

The scans cost between $200 and $300, roughly double the price of a mammogram. Insurers are not covering lung scans because the government does not recommend them.

The biggest weakness in the study is that it lacked a comparison group, making it impossible to tell how people would have fared if they didn't receive a CT scan.

Henschke said the general population can be the comparison group, because lung cancer is so common and its survival odds are so well known. But many scientists disagreed, and said her study falls short for this reason.

"It raises great hope for CT screening," but it doesn't prove a benefit, said Dr. Denise Aberle of the University of California, Los Angeles, who is helping conduct a government-funded study that should give more definitive answers. It is screening 53,000 current and former smokers with CT scans or regular chest X-rays to see whether either can cut lung cancer deaths. The Mayo Clinic also is leading a screening study, and others are under way in Europe.

Until there is proof, patients considering screening should ask their doctors about the pros and cons, said Dr. Joan Schiller, a cancer specialist at the University of Texas Southwestern Medical School.

"They need to know that the chances are good that something abnormal will be found," which could lead to false alarms, she said.

In light of the latest results, at least one patient advocacy group - the Lung Cancer Alliance ¡ª is urging doctors to regularly screen patients for lung cancer.

"This is the most important breakthrough for the lung cancer community that has ever happened," president Laurie Fenton said in a statement.

Research on lung cancer detection may have been delayed because of the stigma associated with the disease ¡ª the notion that smokers brought this on themselves and that little could be done once they developed it, many doctors say. The problem grew worse when X-ray screening studies in the 1970s failed to find a benefit, Dr. Michael Unger of the Fox Chase Cancer Center in Philadelphia wrote in an accompanying editorial.

Henschke's latest study is a "provocative, welcome salvo in the long struggle to reduce the tremendous burden of lung cancer on society," Unger wrote.

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