• Department of Radiology, Duke University Health System, Durham, North Carolina; Present Address: Department of Radiology, Seoul St. Mary's Hospital, College of Medicine, The Catholic University of Korea, Seoul, Republic of Korea.
• Department of Biostatistics and Center for Statistical Sciences, Brown University School of Public Health, Providence, Rhode Island.
• Department of Radiology, Seoul National University College of Medicine, Seoul, Republic of Korea.
• Department of Radiology, Research Institute & Hospital, National Cancer Center, Goyang, Republic of Korea.
• Department of Radiology, Duke University Health System, Durham, North Carolina; Department of Pharmacology and Cancer Biology, Duke University Health System, Durham, North Carolina. Electronic address: patz0002@mc.duke.edu.

INTRODUCTION: To determine the clinical significance of CAT3 abnormalities and the necessity of a six-month follow-up CT. We also explored features associated with increased lung cancer risk.

METHODS: From the NLST database, we identified participants with CAT3 lesions at prevalence screen. Rates of lung cancer and lung cancer-specific deaths (LSD) were compared between those who underwent first follow-up CT before six months (Early Diagnostic Group, EDG) and those who underwent annual screening (Annual Diagnostic Group, ADG). We estimated the change in LSD if the 6-month-CT was eliminated. Regression analysis was performed to identify features associated with CAT3 participants who developed lung cancer.

RESULTS: 1763 CAT3s were identified (6.6% of all LDCT participants), with a total of 108 lung cancers (6.1 %) and 41 LSDs (2.3 %) over seven-year period. Rates of lung cancer (7.5 vs. 3.1 %) and LSD (4.0 vs. 1.0 %) were higher in EDG than in ADG. We estimated an increase in LSD of 0.6 % of all CAT3 participants (24.4 % of all LSDs) if the 6-month-CT was not performed. Multivariate regression analysis found increased age, emphysema, and a part-solid nodule >5 mm were associated with CAT3 participants who developed lung cancer.

CONCLUSIONS: CAT3 lesions are uncommon and eliminating the 6-month-CT would potentially increase LSD by 0.6% of all CAT3 patients. Age, emphysema, part-solid nodule >5 mm may be useful in risk prediction models to determine which CAT3 participants are more likely to develop lung cancer, and suggest which patients may need more intense follow-up.