Spiral CT Lung Scans for Smokers and Former Smokers

The introduction in the 1990s of a high-tech procedure for scanning the lungs of smokers and former smokers raised hopes that it would spare many of them a lung cancer death. A new study reported in the journal Radiology, however, confirmed the fears of a few physicians who have publicly questioned the premature promotion of this test. Its potential for harm has been verified in the study conducted by researchers at the Mayo Clinic in Rochester, Minnesota.

The spiral computed tomography, or CT, lung scan provides three-dimensional images that allow doctors to find many more tiny lung nodules than would be apparent on the standard chest x-ray. And that is the problem. The high number of nodules and other lung abnormalities found in this new study required extensive investigation and, in many instances, risky surgery before most of them could be classified as benign. This high rate of false alarms can be justified only by a screening test that offers a substantial reduction in lung cancer deaths. And the jury is still out on this important point.

Too Many False Alarms

Funded by the U. S. National Cancer Institute, the study included over 1500 men and women who were given annual CT lung scans. 61% of them were current smokers and the rest were former smokers. After five years, the research team led by Stephen J. Swensen , MD, at the Mayo Clinic in Rochester , Minnesota , found that the false-positive (false-alarm) rate was extremely high. Nodules—749 altogether—that proved to be benign were found in 69% of the participants. In some cases, the lung abnormalities proved to be cancer, but they were a type that would never produce symptoms or become life-threatening.

 “Intervention for benign nodules is common and has substantive financial, mortality, morbidity, and quality of life costs,” wrote Dr. Swensen and colleagues. A lung biopsy, for example, is a potentially risky procedure that is typically ordered to rule out lung cancer. A small amount of lung tissue is removed through a telescope-like tube that is inserted down the windpipe (a bronchoscopy) or via a needle inserted through the chest wall. Occasionally, a larger amount of lung tissue must be biopsied which requires major surgery (thoracotomy or thoracic surgery), with the potential for severe complications in people with ailments common to smokers, such as heart or lung diseases.   

Lifesaving Benefit Unproven

Here are the Mayo Clinic study's conclusions: “Screening for lung cancer offers the possibility of reducing mortality from lung cancer. Our preliminary results do not support this possibility and may raise concerns that false-positive results and overdiagnosis could actually result in more harm than good.” They explained overdiagnosis as the detection of slow-growing lung cancers that “a patient dies with and not from,” a phenomenon that is not limited to the lungs. The breast, prostate, thyroid and other organs also contain cancers that would never become symptomatic or deadly if they went undiscovered.

Researchers suspect overdiagnosis whenever a study like this one finds a high number of early-stage would-be cancers but no reduction in the number of people diagnosed with more advanced disease. This strongly suggests that the overwhelming majority of these suspicious abnormalities would never have progressed to fatal lung cancer.

The study was not designed to come to a conclusion regarding the ability of the CT scan to reduce the rate of lung cancer deaths because there were no unscreened participants to serve as a comparison to the people given lung scans. There were only nine lung cancer deaths but 40 deaths from other causes. The investigators, however, point out that the lung cancer death rate was similar to that of an earlier study called the Mayo Lung Project.

The definitive answer regarding the spiral CT scan's potential contribution to reducing the lung cancer death rate is expected from another National Cancer Institute- financed project called The National Lung Screening Trial. This is the first trial to compare the new technology with the old. 50,000 current or former smokers have already been enrolled. They have been randomly assigned to receive either a chest x-ray or a CT lung scan. After one or two years, each group will have the same screening procedure again. Results will not be published before 2010.

Trial Sponsor Issues Warning

The National Cancer Institute warns about the risks of screening on its Web site:

“Conventional wisdom suggests that the smaller the tumor, the more likely the chance of survival. But no scientific evidence to date has shown that screening or early detection of lung cancer actually saves lives. The National Lung Screening Trial, because of the large number of individuals participating and because it is a randomized, controlled trial, will be able to provide the evidence needed to determine whether spiral CT scans are better than chest   X-rays at reducing a person's chances of dying from lung cancer.”

Maryann Napoli, Center for Medical Consumers © May 2005