Definition of a positive test result in computed tomography screening for lung cancer: a cohort study

Low-dose computed tomography screening for lung cancer can reduce mortality among high-risk persons, but "false-positive" findings may result in unnecessary evaluations with attendant risks. The effect of alternative thresholds for defining a positive result on the rates of positive results and cancer diagnoses is unknown.

To assess the frequency of positive results and potential delays in diagnosis in the baseline round of screening by using more restrictive thresholds.

Prospective cohort study.

Multi-institutional International Early Lung Cancer Action Program.

21 136 participants with baseline computed tomography performed between 2006 and 2010.

The frequency of solid and part-solid pulmonary nodules and the rate of lung cancer diagnosis by using current (5 mm) and more restrictive thresholds of nodule diameter.

The frequency of positive results in the baseline round by using the current definition of positive result (any parenchymal, solid or part-solid, noncalcified nodule ≥5.0 mm) was 16% (3396/21 136). When alternative threshold values of 6.0, 7.0, 8.0 and 9.0 mm were used, the frequencies of positive results were 10.2% (95% CI, 9.8% to 10.6%), 7.1% (CI, 6.7% to 7.4%), 5.1% (CI, 4.8% to 5.4%), and 4.0% (CI, 3.7% to 4.2%), respectively. Use of these alternative definitions would have reduced the work-up by 36%, 56%, 68%, and 75%, respectively. Concomitantly, lung cancer diagnostics would have been delayed by at most 9 months for 0%, 5.0% (CI, 1.1% to 9.0%), 5.9% (CI, 1.7 to 10.1%), and 6.7% (CI, 2.2% to 11.2%) of the cases of cancer, respectively.

This was a retrospective analysis and thus whether delays in diagnosis would have altered outcomes cannot be determined.

These findings suggest that using a threshold of 7 or 8 mm to define positive results in the baseline round of computed tomography screening for lung cancer should be prospectively evaluated to determine whether the benefits of decreasing further work-up outweigh the consequent delay in diagnosis in some patients.