CT screening for lung cancer: suspiciousness of nodules according to size on baseline scans.

Purpose: To assess the frequency with which a particular, possibly optimal work-up of noncalcified nodules less than 5.0 mm in diameter identified on initial computed tomographic (CT) images at baseline screening leads to a diagnosis of malignancy prior to first annual repeat screening, compared with a possibly optimal work-up of larger nodules.

Materials And Methods: Two series of baseline CT screenings in high-risk people were retrospectively reviewed. The first series (n = 1,000) was performed in 1993-1998; the second (n = 1,897), in 1999-2002. In each series, cases in which the largest noncalcified nodule detected was less than 5.0 mm in diameter and those in which it was 5.0-9 mm were reviewed to determine whether diagnostic work-up prior to first annual repeat screening showed or would have shown nodule growth and led or would have led to a diagnosis based on biopsy or surgical specimens.

Results: The frequency with which malignancy was or could have been diagnosed when the largest noncalcified nodule was less than 5.0 mm in diameter was 0 of 378, whereas when the largest noncalcified nodule was 5.0-9 mm in diameter, the frequency was 13 or 14 of 238. If persons with only nodules smaller than 5.0 mm had merely been referred for first annual repeat screening without immediate further work-up, the referrals for such work-up would have been reduced by 54% (from 817 [28%] to 385 [13%] of 2,897).

Conclusion: In modern CT screening for lung cancer at baseline, detected noncalcified nodules smaller than 5.0 mm in diameter do not justify immediate work-up but only annual repeat screening to determine whether interim growth has occurred.