False Positives Mar Lung CT Screens

Physicians have lamented for decades the absence of a reliable screening test for lung cancer, and they’re going to have to hum that tune awhile longer since the latest study of chest CT confirms previous findings: the test has an unacceptably high false positive rate.

The disappointing findings were reported by the NIH’s Jennifer Croswell at the recently completed 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,” Croswell told MedPageToday.

In Croswell’s blandly named Lung Screening Study, 1,610 participants received a baseline CT and 1,580 got a chest X-ray. Both groups received a repeat imaging study a year hence and were followed for another year.

The scientists defined a positive test as one revealing a noncalcified nodule at least four millimeters in diameter, or any other finding that was suspicious for cancer.

They defined false positives as positive screens that prompted a negative work-up or that resulted in no cancer diagnosis 12 months later.

The false positive rate for participants receiving CT scans was 21% after the first image and 33% after the second.  It was 9% and 15% for those receiving chest x-rays.

In the CT group, false positives tests prompted invasive diagnostic procedures and major surgeries in 6.6% and 1.6% of the participants, respectively. Those numbers were 4.2% and 1.9% for false positives resulting from a chest X-ray.

According to Peter Bach of the Memorial Sloan-Kettering Cancer Center in New York, “nothing really changes here,” as a result of the new study. “There is no organization in the world that recommends screening for lung cancer with CT,” or any other technique, Bach told MedPageToday.

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