ROCHESTER, Minnesota—In a Mayo Clinic study of low-dose helical CT screening for lung cancer, nearly 70% of the study participants had one or more suspicious lung nodules, but only 1.4% of all nodules proved to be malignant. The other 98.6% were benign "and therefore were false-positive findings," said lead investigator Stephen J. Swensen, MD, professor of radiology. The results, he said, offer reasons for optimism as well as reasons for doubt that CT screening for lung cancer will ultimately save lives by reducing disease-specific mortality.
The preliminary results of the ongoing phase II study included 1,520 current or former smokers age 50 years and older. Study participants had to have at least 20 pack-years of smoking; those who no longer smoked had to have quit within the previous decade. All were asymptomatic for lung cancer.
At the end of 3 years of screening, the researchers are following more than 2,800 uncalcified, radiologically indeterminate lung nodules. To date, eight participants have had surgery for removal of a benign nodule, accounting for about 20% of all operations in the series (Am J Roentgenology 179:833-836, 2002).
Recent data from other studies of CT screening for lung cancer show that about half of all nodules removed are benign, he added. Such false-positive rates, Dr. Swensen observed, "would be clearly unacceptable for a mass screening endeavor." The cost alone of the unnecessary operations would make such screening unacceptable, but of greater concern, he said, "are the morbidity and the 3.8% mortality seen with wedge resections of lung nodules in community hospitals in the United States."
Reason for Optimism
In the Mayo study, 41 lung cancers have been found to date, of which 59% were stage IA. In contrast, Dr. Swensen noted, the current rate of stage IA cancers at diagnosis in clinical practice is 15% to 20%. "Survival of patients with stage I lung cancers is 60% to 70%," he noted. Thus, "there is reason for hope," he said, that CT screening could prove cost-effective in preventing lung cancer deaths.
James L. Mulshine, MD, head, Experimental Intervention Section, Cell and Cancer Biology Branch, Center for Cancer Research, National Cancer Institute, in an interview with ONI, said that he appreciated Dr. Swensen’s discussion of the problems encountered with CT screening for lung cancer. "Yet at the end of the day," he said, "they did actually do quite well in finding a very high frequency of stage I, potentially curable cancers. But it just was an enormous effort to get there."
