Clinical Significance of Lung-RADS Category 3 Lesions in the National Lung Screening Trial

IntroductionTo determine the clinical significance of category 3 (CAT3) abnormalities and the necessity of a 6-month follow-up computed tomography (CT). We also explored features associated with increased lung cancer risk.MethodsFrom the National Lung Screening Trial database, we identified participants with CAT3 lesions at prevalence screen. Rates of lung cancer and lung cancer-specific deaths (LSDs) were compared between those who underwent first follow-up CT before 6 months (early diagnostic group) and those who underwent annual screening (annual diagnostic group). We estimated the change in LSD if the 6-month CT was eliminated. Regression analysis was performed to identify features associated with participants with CAT3 who developed lung cancer.ResultsA total of 1763 CAT3s were identified (6.6% of all participants who had low-dose CT), with 108 lung cancers (6.1%) and 41 LSDs (2.3%) in a 7-year period. Rates of lung cancer (7.5% versus 3.1%) and LSD (4.0% versus 1.0%) were higher in the early diagnostic group than in the annual diagnostic group. We estimated an increase in LSD of 0.6% of all participants with CAT3 (24.4% of all LSDs) if the 6-month CT was not performed. Multivariate regression analysis found that increased age, emphysema, and a part-solid nodule greater than 5 mm were associated with participants with CAT3 who developed lung cancer.ConclusionsCAT3 lesions are uncommon, and eliminating the 6-month CT would potentially increase LSD by 0.6% of all patients with CAT3. Age, emphysema, and part-solid nodule greater than 5 mm may be useful in risk prediction models to determine which participants with CAT3 are more likely to develop lung cancer and suggest which patients may need more intense follow-up.