Annual CT scans of current and former heavy smokers reduce the risk that they will
die from lung cancer by 20 percent, a huge government-financed study has found.
The finding, announced by the National Cancer Institute on Thursday, represents a major advance in cancer detection that could potentially save thousands of lives annually, although at considerable expense. Lung cancer claims about 160,000 lives each year, more than the deaths from colorectal, breast, pancreatic and prostate cancers combined. In most patients, the disease is discovered too late for effective treatment, and 85 percent of those who are diagnosed with lung cancer die from it.
Until now, no screening method had proven to be effective at reducing mortality from the disease. Four randomized, controlled trials done during the 1970s showed that chest X-rays helped to catch cancers at an earlier stage, but had no effect on overall death rates. Since then, researchers have suggested that CT scans — which use coordinated X-rays to provide three-dimensional views of body tissue — could detect lung tumors at an even earlier stage than X-rays could, but no trial had shown conclusively that deaths could be averted.
“This is the first time that we have seen clear evidence of a significant reduction in lung cancer mortality with a screening test in a randomized controlled trial,” said Dr. Christine Berg of the National Cancer Institute.
The trial, called the National Lung Screening Trial, involved more than 53,000 current and former heavy smokers between the ages of 55 and 74 who were given either a standard chest x-ray or a low-dose CT scan at the start of the trial and then twice more over the next two years. The participants were followed for up to five years, and their deaths counted. There were 354 lung cancer deaths among those who received CT scans, and 442 lung cancer deaths among those who got conventional X-rays.
Dr. Claudia Henschke, a longtime advocate for use of CT scans to screen for lung cancer, said the study probably underestimated the benefits of CT scans, because participants in the study were screened only three times over two years. Had the screening continuing annually for 10 years, as many as 80 percent of lung cancer deaths could have been averted, she said.
“What we also have found is that low-dose CT scan gives information on cardiovascular disease, emphysema and other pulmonary diseases,” Dr. Henschke said. “Those are the three big killers of older people. There is just tremendous potential.”
But Dr. Edward F. Patz Jr., professor of radiology at Duke University who helped to design the study, said he was far from convinced that a thorough analysis of the study would show benefits from widespread CT screening in preventing lung cancer deaths. Dr. Patz said that the biology of lung cancer indicates that the size of cancerous lung tumors tells little about the stage of the disease.
“If we look at this study carefully, we may suggest that there is some benefit in high-risk individuals, but I’m not there yet,” Dr. Patz said.
Since there are more than 80 million current and former smokers in the United States, a widespread screening program of at-risk individuals would be enormously costly. Low-dose CT scans also expose patients to considerably more radiation than standard chest X-rays do, and little is known about how the cumulative risks of years of such scans would balance out with the benefits of the information they provide. Also, more scans would also mean more false positive results, leading to more additional tests and surgical procedures performed on people who do not turn out to have any disease, further complicating the picture.