Lung cancer screening by low-dose computed tomography results in high rate of false positives

1 Jun 2009

Researchers from the National Institutes of Health (NIH), presenting at the American Society of Clinical Oncology annual meeting, have shown that patients who undergo lung cancer screening with low-dose computed tomography (LDCT) are at high risk for receiving false-positive results.

Several studies evaluating whether lung cancer screening reduces cancer deaths have reported a high incidence of noncalcified nodules (round lesions of unknown cause) among those screened. However, this study marks the first time that the cumulative risk of a false-positive result has been quantified.

The study included 1,610 patients who underwent LDCT screenings and 1,580 who underwent chest x-ray. Participants were between 55 and 74 years old and current or former smokers. They underwent a baseline screening exam, a follow-up exam at one year, and were followed for an additional year. For a patient choosing to undergo LDCT, the risk of obtaining a false-positive result is 21 per cent after one scan and 33 per cent after a second. Patients choosing to undergo chest x-ray screening have a false-positive risk of 9 per cent after one test and 15 per cent after two. False-positive results were defined as noncalcified nodules greater than or equal to 4 mm or other findings that indicated a suspicion of cancer that were later found to be noncancerous.

Of the patients who had false positives, slightly more than half underwent follow-up imaging exams. In the LDCT group, 6.6 per cent of patients with false positives underwent invasive diagnostic procedures and 1.6 per cent had major surgery. In the x-ray group, 4.2 per cent of patients with false positives underwent invasive follow-up procedures and 1.9 per cent of the total patients in this group had major surgery. Complication rates for patients who had invasive procedures were low, but a few patients had to be hospitalised for a collapsed lung or blood in the lung (less than 1 per cent), and another 1 per cent had to be given antibiotics for infections.

"All medical interventions – including screenings – have not only the potential to benefit patients but also the potential for harm," said Dr. Jennifer M. Croswell, Acting Director of the NIH Office of Medical Applications of Research and the study’s lead author. "We want to give people who are considering lung cancer screening the information they need to make informed decisions about the tests they choose. False-positive results may create increased psychological stress in patients and an increased burden on the healthcare system."

Findings from the study indicated that patients who were current smokers or older than 64 years of age might have an increased risk of false positives, but because the sample sizes were small, the researchers say more studies are needed to confirm those findings.