The potential use of imaging tests like CT to screen for lung cancer has been the subject of lively debate in recent years. Some previous studies have suggested that such tests can find lung cancer earlier, when tumors are smaller and more likely operable. The question is whether this translates into helping people live longer and whether it has an adverse affect on their quality of life.

In the latest study, researchers looked at the CT scans of more than 3,200 adults with a history of smoking but no symptoms of lung cancer. As before, the imaging procedure was shown to find smaller tumors earlier, but the researchers saw no corresponding evidence that patients lived longer as a result of early detection and treatment.

Without such a benefit to justify the approach, the researchers warn, we are left with the prospect of taking people who have no symptoms of disease and subjecting them unnecessarily to the costs, pain, inconvenience, and health risks associated with additional scans, surgeries, recuperation, etc.

More research is needed to determine if people who show no symptoms of lung cancer should get the screens, the study concludes. "These findings . . . raise doubts about the premise underpinning CT screening for lung cancer, and also raise concerns about its potential harms if pursued on a wide scale," write the study authors.

The research team was led by Peter Bach, MD, MAPP, of Memorial Sloan-Kettering Cancer Center in New York City. The report appears in the latest issue of JAMA, the Journal of the American Medical Association.

Lung cancer accounts for 25% of cancer-related deaths and 6% of all deaths in the US.

Cancer experts say the new study serves as a 'reality check' for those who felt a study published by the New England Journal of Medicine in October was proof enough that lung cancer screening saves lives. That study reported that CT screening of adults at high risk of lung cancer could prevent 80% of lung cancer deaths.

Neither study was based on a randomized, controlled trial,a gold standard for research that helps set public health standards. An editorial accompanying the JAMA study insists only randomized, controlled trials can answer the question of whether screening can catch lung cancer early enough to save more lives. Both studies point to the need for such trials to better clarify the pros and cons of lung cancer screening, write William Black and John Baron, both MDs at Dartmouth Medical School in New Hampshire.

"Although expensive and time-consuming, rigorous trials of cancer screening are far more cost effective than what might be the alternative -- widespread adoption of costly screening interventions that cause more harm than good," Black and Baron say.

In a randomized, controlled study, people are randomly assigned to one of two groups: those who are screened (screening group) and those who are not screened (control group). This allows researchers to compare the two groups over time to see if one does better than the other. These types of studies are a more accurate way to tell if screening helps people live longer, for example, or if it results in more unneeded complications.

Such rigorous studies are now under way in the US and in Europe. They should offer better answers to these questions in the coming years.

The new study is based on the results of CT scans done at three separate academic hospitals on more than 3,200 people with a history of smoking but no symptoms of lung cancer. Researchers examined the number of lung cancers diagnosed, the number of surgeries performed, and number of deaths that occurred in those who were screened. They compared these to numbers that would be expected based on mathematical models of people in this risk group who were not screened.

The researchers found no reduction in lung cancer deaths among those who got the scans. But there was a 3-fold increase in lung cancer diagnosis compared to what would be expected when not having the scans, and there was a 10-fold increase in lung cancer surgeries compared to not having the scans.

At the end of the 4-year study period, there were 38 deaths that occurred from lung cancer, compared to 39 deaths that would be expected to occur without CT scans.

The newer findings are in line with the American Cancer Society's position that there is not adequate scientific evidence to support lung cancer screening at this time, says Robert Smith, PhD, director of screening for the Society. Smokers and former smokers should talk to their doctors about their cancer risks and screening options.

Len Lichtenfeld, MD, the American Cancer Society's deputy chief medical officer, says CT scanning (and especially a newer, faster scan known as spiral CT) is sensitive enough to find small tumors and other nodules, so it offers hope as an important prevention and detection tool, much like mammography is used to screen for breast cancer. But that hope remains elusive until more research is done to prove screening's benefits.

"More recent evidence suggests that in fact there may be lung cancers present which do not cause a person significant problems through their lifetimes," Lichtenfeld writes in his Web log, Dr. Len's Cancer Blog. "The problem is that we can end up treating many more people than really necessary to help a few."

Finding a lung cancer when it's smaller does not guarantee a patient will be saved by treatment, Smith and Lichtenfeld say.

Critics of using CT scans for lung cancer screening are simply not looking far enough ahead to see the benefits, says Claudia Henschke, MD, PhD, lead author of the New England Journal of Medicine study and an imaging test researcher at New York Hospital-Cornell Medical Center.

Henschke criticizes the Bach team for relying on a mathematical model that she says downplays the lifesaving potential of CT scans up to and beyond 4 years.

"In the earliest years after initiation of screening, no reduction in deaths can be expected," Henschke says.

Citation: 'Computed tomography screening and lung cancer outcomes.' Published March 7, 2007, in JAMA. First author: Dr. Peter B. Bach, Memorial Sloan-Kettering Cancer Center, New York.