Diagnostic Performance of the Modified Lung CT Screening Reporting and Data System in a TB-Endemic Country: The Korean National Lung Cancer Screening Program.

Background: In 2019, Korea initiated the world's first national low-dose CT imaging lung cancer screening (LCS) program, adapting the Lung CT Screening Reporting and Data System (Lung-RADS) to counteract the high false-positive rates driven by prevalent TB.

Research Question: Does the modified Lung-RADS enhance screening specificity while maintaining sensitivity?

Study Design And Methods: This nationwide, retrospective cohort study included high-risk individuals aged 54 to 74 years with active tobacco use of at least 30 pack-years participating in the national LCS program from 2019 through 2020. The modified Lung-RADS 1.0 introduced category 2b for nodules matching the size of categories 3 or 4, but showing benign features like granulomas and juxtapleural nodules, and enhanced details for category 4X. Lung cancer diagnosis rates within 1 year of screening and the diagnostic performance of the modified and original Lung-RADS were evaluated.

Results: Among 152,918 participants (98.2% male; mean [SD] age, 61.7 [5.3] years), lung cancer was diagnosed in 0.68% of participants (1,047 of 152,918). A linear trend in cancer rates across Lung-RADS categories was noted (P < .001). Category 2b showed a higher cancer rate than category 2 (0.25% [45 of 18,120] vs 0.14% [33 of 23,467]; P = .01), but lower than category 3 (0.53% [37 of 7,009]; P = .001). Category 4X showed a cancer rate of 36.88% (416 of 1,128). The modified Lung-RADS demonstrated improved specificity (91.96% [139,664 of 151,871] vs 80.06% [121,589 of 151,871]; P < .001) compared with the original criteria. Although sensitivity showed a modest decrease (81.9% [858 of 1,047] vs 86.2% [903 of 1,047]; P < .001), the modification substantially reduced the follow-up burden, decreasing the number of positive screening results needed to detect 1 case of cancer from 34.5 to 15.2. The positive predictive value improved significantly (from 2.90% [903 of 31,185] to 6.57% [858 of 13,065]; P < .001), whereas the negative predictive value remained consistently high (modified, 99.86% [139,664 of 139,853] vs original, 99.88% [121,589 of 121,733]; P = .23).

Interpretation: Our results show that Korea's modified Lung-RADS enhanced screening efficiency through improved specificity, despite a small reduction in sensitivity.