News that annual CT lung scans can reduce the risk of lung cancer death among former and current heavy smokers was celebrated by national heath officials this month. A major government study found the screening scans saved the life of one person for every 300 current or former smokers who were scanned.
But now cancer and screening experts are worried that the limited findings will be used by private screening centers to promote the test to a broader group than was studied. That, in turn, could lead to thousands of unnecessary lung scans, causing excess radiation exposure and unnecessary biopsies and surgery.
Dr. Otis W. Brawley, chief medical officer of the American Cancer Society, said he was stunned to hear a radio advertisement for an Atlanta screening center cite the study just a few days after the government had announced the results. The wording of the ad seemed to be aimed at a broad group, ranging from heavy smokers to women who had never smoked, Dr. Brawley said.
"We really need to weigh the harms associated with screening," he said. "The scientific community still needs to digest this. To take a trial that involves people at high risk for lung cancer and to extrapolate it and say it's good for people with intermediate or low risk is not appropriate."
The study, called the National Lung Screening Trial, focused on a specific high-risk group: 53,000 current and former heavy smokers, aged 55 to 74, who had smoked for at least 30 pack-years. That means someone who smoked one pack a day for 30 years, two packs a day for 15 years or three packs a day for at least 10 years would qualify for the study.
Former smokers who had accumulated 30 pack-years were included only if they had stopped smoking within the previous 15 years.
The smokers and former smokers were given either annual CT lung scans or chest X-rays. Compared with conventional X-rays, the CT, or computed tomography, scans create a detailed three-dimensional image of the lungs. The study was stopped when it was found that the scanning group had a 20 percent lower risk of dying from lung cancer than those being screened with X-rays.
But the early results also showed a downside of scanning: one of every four lung scans showed an abnormality, which often led to additional worry, radiation exposure from follow-up scans and, sometimes, lung biopsies and even risky surgery. But because the study was stopped early, a full analysis of the harms caused by screening scans is still months away.
Reading the scans is tricky because harmless nodules can be misinterpreted as suspect lesions. In the study, even experienced radiologists at major cancer centers had a high rate of false positives, suggesting that the rate would be even higher in the real world.
"There is a learning curve to reading spiral CTs," Dr. Brawley said. "I'm concerned that some radiologists might be early in that learning curve and some patients may be harmed because of it."
While the study found a benefit to scanning a specific group of high-risk smokers, that doesn't mean other groups will get the same benefit, says Dr. Peter B. Bach, a pulmonologist at Memorial Sloan-Kettering Cancer Center in New York. In lower-risk groups, for instance, it's likely that thousands of people would need to be exposed to the risks of screening before a single life was saved. And it's possible that many of those scanned unnecessarily could be seriously harmed.
"The aggregate harms to all the people's lives who are not saved have to be taken into account," Dr. Bach said. "Even in these highly controlled settings, about 1 percent of the people had surgery or a part of their lung removed for something they thought was cancer and it wasn't."
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http://well.blogs.nytimes.com/2010/11/15/the-downside-of-a-cancer-study-extolling-ct-scans/
