OBJECTIVE: We aimed to examine the prevalence and clinical outcomes of atypical pulmonary cysts (APCs) in lung cancer screening (LCS) and evaluate the impact of APC introduction on Lung-RADS v2022 categorization. MATERIALS AND METHODS: We reviewed 2968 low-dose baseline chest CT scans from LCS participants between June 2017 and April 2023. Two thoracic radiologists assessed the presence and type of APCs and evaluated interval changes. We also investigated how the introduction of APC changed Lung-RADS categories. Interobserver agreement was assessed using Cohen's kappa coefficient. RESULTS: Of the 2968 participants (2900 men, 68 women
median age: 61 years [IQR: 57-65]), 18 (0.6%) had APCs. The interobserver agreement for APC presence was fair (κ = 0.33
95% CI: 0.07-0.44). Among the 16 APC cases with follow-up CTs (median follow-up: 22 months), lung cancer was confirmed in three cases (18.8%). Among the remaining 13 APCs, 4 (30.8%) showed growth, 7 (53.8%) showed no change and 2 (15.4%) exhibited decreased wall thickness. Histological confirmation was not obtained for these 13 cases, indicating a minimum cancer rate of 18.8%. The introduction of APC led to a positive result change in 0.4% of participants (12/2968), with two lung cancer cases among them. CONCLUSION: APCs were infrequent in LCS, with a 0.6% prevalence, but had a high cancer rate (18.8%). Although the introduction of APC led to a 0.4% increase in positive screenings, this is considered acceptable as it included two lung cancer cases, highlighting the importance of recognizing APCs for early lung cancer detection. KEY POINTS: Question What is the prevalence and clinical significance of APCs detected during LCS, and how do they impact diagnostic outcomes? Findings APCs were detected in 0.6% of participants, with a high cancer rate of at least 18.8%, and increased screening positive results by 0.4%. Clinical relevance APCs during LCS, although uncommon, are crucial because of their high risk of lung cancer. This enhances early detection of lung cancer and improves patient management strategies.