June 29, 2011 — Screening smokers and former smokers for lung cancer with low-dose CT imaging saves lives, a huge, decade-long study shows, but experts say it is too soon to recommend screening for everyone at risk.
Heavy smokers and former smokers who had the CT imaging were 20% less likely to die of lung cancer than smokers who got traditional chest X-rays.
Results from the National Lung Screening Trial, which included more than 53,000 people, were reported Wednesday in the New England Journal of Medicine.
The study is the first to show that screening can reduce lung cancer mortality by finding tumors early. But many questions remain, including who should have the test and at what cost to the health care system.
“We now know that it is possible to reduce deaths from lung cancer with low-dose CT, and now we need to figure out what to do with this knowledge,” Dartmouth Medical School professor of medicine Harold C. Sox, MD, tells WebMD. “There are about 94 million smokers or former smokers in the United States, and screening even a portion of them would be very expensive.”
CT Scans vs. X-Rays
Beginning in the summer of 2002, more than 53,000 heavy smokers and former heavy smokers between the ages of 55 and 74 were enrolled in the study at 33 sites across the country.
The participants were randomly assigned to receive three annual screenings with either low-dose spiral CT or standard chest X-ray.
A traditional X-ray produces a single image of the chest, while spiral CT involves multiple, three-dimensional images of the chest cavity.
Studies show standard X-ray screening to be somewhat effective for identifying lung cancers, but it has never been shown to reduce deaths from the disease.
During the screening phase of the trial, 39% of the low-dose CT participants and 16% of the standard X-ray group had at least one positive screening result; more than nine out of 10 positive tests in the first round of screening led to further diagnostic testing.
Rate of False-Positives
In both groups, 95% or more of these suspicious early screens turned out to be false positives.
This was usually confirmed with follow-up CT scans, which showed no change over time. But in some cases the false-positive readings also led to more invasive testing, including PET imaging, lung biopsy, and exploratory lung surgery.
Study researcher Christine Berg, MD, of the National Cancer Institute, tells WebMD that the complication rate from the initial screening and the invasive follow-up testing was very low.
Low-dose CT delivers much less radiation than a traditional chest CT, but the potential long-term risks of screening, including follow-up of false positives with higher-radiation imaging, could not be measured in the study.
“The data are telling us that the benefits of screening outweigh the risks in this population of heavy smokers and former smokers in this particular age group,” Berg says.
The finding of a 20% reduction in lung cancer deaths was so impressive that an independent monitoring board stopped the study last year.
Cost of Screening
The researchers estimate that about 7 million Americans meet the qualifications for screening under the study guidelines. The cost of screening just these smokers and former smokers would easily reach billions of dollars a year.
The National Lung Screening Trial researchers are conducting a cost analysis of the study data to present to health policy makers. Berg says the analysis may be completed by the end of the year.
University of Michigan professor of radiology Ella Kazerooni, MD, says questions will remain about the costs vs. benefits of population-wide lung cancer screening even after the analysis is complete.
Kazerooni chairs the American College of Radiology Panel on Thoracic Imaging and she was a study investigator.
“The study participants were 55 to 74 at enrollment, so we can’t really say whether screening is effective for younger smokers or older ones,” she tells WebMD.
Risks vs. Benefits
A single low-dose CT scan costs around $300, and smokers and former smokers who want the test now will probably have to pay for it themselves.
“The message right now would have to be ‘Let the buyer beware,'” Kazerooni says. “Someone who gets this test has about a 40% chance of having additional tests, and only a very small minority of these people will have lung cancer.”
CT screening was not found to reduce deaths from small-cell lung cancer, a particularly aggressive form of the disease that account for 10% to 15% of lung cancers.
There is also concern that population-wide screening could lead to overdiagnosis and overtreatment of lung cancers in the same way that PSA screening has led to overdiagnosis of prostate cancers, Sox says.
In an editorial published with the study, Sox noted that the National Lung Screening Trial data as well as other studies suggest that some lung cancers grow so slowly that they may never cause harm.
Sox says smokers and former smokers should learn as much as they can about the pros and cons of screening before having the test.
“I would recommend scheduling a half-hour consult with your doctor to really weigh the benefits and risks in detail,” he says.