CT Lung Cancer Screening Yields High False-Positive Rate

CT Lung Cancer Screening Yields High False-Positive Rate

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
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."


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