CT Lung Cancer Screening Leaves a Trail of False Positives

ORLANDO, Fla., May 30, 2009— -- A high-tech scanning technique that doctors hoped to use for fast, reliable lung cancer screening has turned out to do its job too well.

Low-dose computed tomography, or CT for short, discovers all sorts of abnormalities in patients' lungs, but produces false positive results for cancer a third of the time, according to a new study.

That's more than twice the false positive rate for standard chest x-rays, and it's not good news for patients, Dr. Jennifer Croswell of the National Institutes of Health said at the annual meeting of the American Society of Clinical Oncology.

"False positive results may create increased psychological stress in patients and an increased burden on the healthcare system," she said.

A false positive may also result in more invasive -- and potentially dangerous -- follow-up tests, she said.

The findings are based on the Lung Screening Study, a randomized trial involving 3,000 patients that examined the feasibility of a large-scale trial of different screening methods, in particular, a head-to-head comparison of CT scans versus regular X-rays.

That larger study, the National Lung Screening Trial, is currently under way and involves 50,000 patients. A similar large study in Europe -- dubbed NELSON -- reported some positive preliminary results earlier this year.

In this study, Croswell reported, 1,610 participants were offered a baseline CT and 1,580 were offered a baseline chest x-ray, with one repeat annual screening. They were followed for a year after their final screen.

A false positive was defined as either a positive screen for lung cancer that was proved false by a complete workup, or by at least 12 months of follow-up with no cancer diagnosis.

By the end of the second screening, CTs had turned up false positives in 33 percent of the patients, compared to 15 percent for standard chest x-rays, the researchers reported.

Of those with false CT positives, 6.6 percent had a more invasive diagnostic test and 1.6 percent had major surgery.