It’s official: CT scans reduce the risk of death for heavy smokers with lung cancer by 20 percent compared to chest X-rays.
After a nearly decade-long study, results from the National Lung Screening Trial were published Wednesday in The New England Journal of Medicine.
The findings made headlines in November 2010 when the National Cancer Institute announced that it had become clear that the group receiving three-dimensional X-ray tests known as low-dose helical CT scans had a significantly higher chance of surviving than those receiving standard chest X-ray tests.
It’s the first type of screening known to reduce the risk of death from lung cancer, despite a high rate of false positive tests from the scans.
“This is enormously important — the most important breakthrough we’ve had in lung cancer research in 50 years,” said Dr. Thomas Lynch, director of the Yale Cancer Center and physician-in-chief at Smilow Cancer Hospital. “Our department is already ramping up to do routine screening on patients who are heavy smokers. I think insurers will be more willing to pay for these procedures and doctors will be more willing to conduct them.”
The trial examined the consequences of the two screening methods on large, randomized populations of heavy smokers ages 55 to 74.
The CT scans were particularly successful at detecting cancer in its early stages in the lining of the lungs and the passages of the respiratory tract. But the CT and X-ray scans were equally unhelpful in detecting small-cell lung cancers, which is an extremely aggressive variety that grows in the tissues of the lung.
“Lung cancer is so aggressive that finding it at a larger and later stage often means that it is incurable,” said Christine Berg, project officer for the trial. “We were very pleased to be able to find this cancer at an early enough stage that we could intervene in some of these cases.”
Adverse events, or harm from the actual screening examinations, were few and relatively minor, she said.
Still, “this is clearly not a home run,” she said.
“In the CT arm of this study, we still have 80 percent of patients who are diagnosed with lung who didn’t benefit from these three rounds of screening,” she said. “We need to improve our imaging.”
The extremely high number of false-positives — or scans indicating a patient may have lung cancer when they actually don’t — could also use some work.
During the screening phase of the trial, nearly 40 percent of participants receiving the CT scans tested positive for lung cancer, but additional tests showed 96.4 percent of them didn’t have it. Most of the false-positive tests were due to the detection of normal lymph nodes or inflamed tissues.
Some worry that the study will lead doctors to over-utilize CT scans, a practice blamed for contributing to skyrocketing health care costs in the United States. There is also concern that repeated exposure to radiation could put patients in unnecessary danger, especially when the false-positive rate is still so high.
But by far, the biggest concern is that heavy smokers will see this as an excuse to not give up the habit, knowing that there may be a scan that could help saves their lives if a cancer develops.
“I do not want the availability of this somewhat-effective screening test to keep someone from quitting smoking,” Berg said. “I think this provides encouragement to people with a persistent risk of lung cancer – that they have the greatest chance of surviving if they quit and catch potential cancer early.”
Additional studies will be conducted in coming months to weigh the benefits against the costs and to see if the findings might apply to additional populations – such as younger and lighter smokers.
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