A new study suggests that screening smokers and former smokers for lung cancer doesn't save lives or prevent advanced disease and may lead to unneeded and harmful treatment.

But it's not the final word.

Some experts have hoped that the scans, a special kind of X-ray that can detect tiny lung abnormalities, will prevent lung cancer deaths by getting people into treatment earlier. But there hasn't been convincing evidence of that.

A large and authoritative scientific study won't be completed for a few years. At present, the American Cancer Society doesn't back the pricey test, and most insurance companies won't pay for it.

New research, appearing in today's Journal of the American Medical Association, analyzed lung cancer deaths and cases of advanced lung cancer among 3,246 smokers and former smokers who had annual CT scans for about four years.

Researchers compared deaths and advanced cancer cases with rates predicted by a mathematical model. The model predicted there would be 33.4 cases of advanced cancer; there were 42. The model predicted 38.8 lung cancer deaths; there were 38.

More surgeries, more risks
''We don't see a trace of evidence that a single life was saved, that a single case of advanced cancer was avoided,'' said co-author Dr. Peter Bach.

CT screening did increase diagnosis and treatment. but Bach said it's likely cancers found by scans were so slow-growing they might never have caused death. And because scans led to more biopsies and surgeries, patients were at risk of complications such as lung punctures, bleeding and infection, he said.

Dr. David Johnson, at Nashville's Vanderbilt-Ingram Cancer Center, who wasn't part of the study, doesn't recommend routine CT scans. ''CT scanning is not the answer," he said. "Stopping smoking is the answer.''