Risk of Malignancy in Cystic Lung Lesions in a Lung Cancer CT Screening Program.

Background There is currently a lack of consensus regarding the risk of malignancy and the natural history of cystic lung lesions. Purpose To evaluate imaging characteristics associated with the risk of malignancy of cystic lung lesions in a lung cancer screening program. Materials and Methods This retrospective study included all CT lung cancer screening examinations performed from January 2015 to July 2023 in a large health care network. Radiology reports were queried for cystic lesions. Baseline CT images were reviewed, and lesion morphologic characteristics and size were recorded. All follow-up CT scans were evaluated for changes in the lesion. The risk of growth and diagnosis of cancer over time were analyzed with Kaplan-Meier curves. Results Among 15 762 patients, 235 were found to have cystic lung lesions; 33 (14%) of these patients were diagnosed with lung cancer arising from the cystic lesion. Increased risk of cancer was associated with nodular wall thickening (odds ratio [OR], 11; P = .002) and presence of a solid nodule (OR, 5.3; P < .001) alone or in combination with a ground-glass component (OR, 24; P < .001). Multilocularity was not associated with an increased risk of cancer (OR, 1.7; P > .2). There were no cases of malignancy in unilocular cystic lesions without wall thickening (n = 46). Lesion growth or increase in complexity over time was associated with an increased risk of malignancy (P < .001). The median time to lesion growth was 636 days. The median time to cancer diagnosis was 482 days, and 28 (85%) of the cancers were stage 0 or I. Conclusion Cystic lung lesions with nodular wall thickening had an increased risk of malignancy. Conversely, unilocular lesions without wall thickening had essentially no risk of malignancy. Most malignant cystic lung lesions exhibited indolent behavior, with slow growth and diagnosis at early stages. © RSNA, 2025 Supplemental material is available for this article. See also the editorial by Zagurovskaya in this issue.