This study was the first in which the CT scan was pitted head-to-head against the standard x-ray. But even though the CT produced a much higher false positive rate, Bach said real-world physicians don't operate on a "yes-no" basis.
For many physicians, the results of a CT scan that showed a minor abnormality might merely lead a doctor to follow a patient more closely.
"All the way through the follow-up scan, the 3-D rendering, even the biopsy, they're all done based on probability, not based on this preconceived notion that the test is positive or negative," he said.
As a result, he was somewhat critical of the study. "The way the authors analyze it -- calling them all positive -- rigs the study toward finding an extremely high false-positive rate," Bach said.
In the end, others say, the future of CT scanning for lung cancer will involve a risk-benefit analysis.
"There is no question that CT screening will detect many lung cancers," said Dr. Martin Edelman of the University of Maryland's Greenebaum Cancer Center in Baltimore and a member of an independent committee verifying results of the NLST.
But so far, there is still a "complete absence of evidence that this approach decreases mortality or morbidity due to lung cancer," he said.
Advocates for screening "have long claimed that there is little or no risk of harm," Edelman added, but Croswell and her colleagues "demonstrate that there is a small, but real potential for harm from screening."
What's more, he said, "the potential for false positivity is highest in those at greatest risk for lung cancer."
The Lung Screening Study was supported by the National Cancer Institute. Croswell did not report any conflicts. Bach has reported financial links with Genentech, Wyeth, Abraxis, Biogen-Idec, and Johnson and Johnson. Edelman has reported financial links with Bristol-Myers Squibb, Cyclacel, Eli Lilly, Genentech, Tragara Pharmaceuticals, Endocyte, Geron, Human Genome Sciences and Schering-Plough.