False-positive Rates in Lung Cancer Screening Increase 33% After Two Exams

Patients screened for lung cancer based on a smoking history potentially face a greater risk of false-positive results following two yearly low-dose computed tomography exams, based on data from the National Lung Screening Trial.

Jennifer M. Croswell, M.D., et al, looked at the data of 3,190 current and former smokers with a history of 30 pack-years or more and no lung cancer. The authors defined a false-positive screening as a positive one with a completed negative work-up or a year or more of follow-up with no cancer diagnosis. The researchers found that the cumulative probability of one or more false-positives from a low-dose CT screening exam increased 21 percent at one year and 33 percent after two years of a screening. The rates for chest x-rays were 9 percent at one year and 15 percent at two.

Noncalcified nodules larger than 3 mm at the T0 CT scan or 4 mm at the T1 scan were considered suspicious, according to the authors. For radiography, suspicious findings included any nodule 3.0 cm or less, masses greater than 3.0 cm, enlarged hilar or mediastinal lymph nodes, major atelectasis, filtrates or consolidation, and pleural masses.

“Given the relatively high probability of a false-positive low-dose CT lung cancer screening examination, it is important that providers have careful discussions with patients who request this technology to help them weigh known harms against currently theoretical benefits,” concluded Croswell et al.

The article, “Cumulative Incidence of False-positive Test Results in Lung Cancer Screening,” was published in the April 20, 2010, Annals of Internal Medicine at www.annuals.org.