• Mallinckrodt Institute of Radiology, Washington University School of Medicine, Box 8131, 510 S. Kingshighway Blvd., St. Louis, MO, 63110, USA. gieradad@wustl.edu.
• National Cancer Institute, 9609 Medical Center Drive, Room 5E108, Bethesda, MD, 20892, USA.
• Department of Biostatistics and Center for Statistical Sciences, Brown University School of Public Health, Providence, RI, 02912, USA.
• University of Colorado School of Medicine, Mail Stop F726, Box 6510, Aurora, CO, 80045, USA.
• Department of Radiology, Northwestern University Feinberg School of Medicine, 676 N. Saint Clair, Suite 800, Chicago, IL, 60611, USA.
• Department of Radiology, University of Michigan Health System, Cardiovascular Center, Room #5482, 1500 East Medical Center Drive, Ann Arbor, MI, 48109, USA.
• Department of Radiology-JTN370, University of Alabama at Birmingham School of Medicine, 619 19th Street South, Birmingham, AL, 35233, USA.
• Department of Radiological Sciences, David Geffen School of Medicine at UCLA, 924 Westwood Boulevard, Suite 420, Los Angeles, CA, 90024, USA.

OBJECTIVES: This study retrospectively analyses the screening CT examinations and outcomes of the National Lung Screening Trial (NLST) participants who had interval lung cancer diagnosed within 1 year after a negative CT screen and before the next annual screen.

METHODS: The screening CTs of all 44 participants diagnosed with interval lung cancer (cases) were matched with negative CT screens of participants who did not develop lung cancer (controls). A majority consensus process was used to classify each CT screen as positive or negative according to the NLST criteria and to estimate the likelihood that any abnormalities detected retrospectively were due to lung cancer.

RESULTS: By retrospective review, 40/44 cases (91%) and 17/44 controls (39%) met the NLST criteria for a positive screen (P < 0.001). Cases had higher estimated likelihood of lung cancer (P < 0.001). Abnormalities included pulmonary nodules ≥4 mm (n = 16), mediastinal (n = 8) and hilar (n = 6) masses, and bronchial lesions (n = 6). Cancers were stage III or IV at diagnosis in 32/44 cases (73%); 37/44 patients (84%) died of lung cancer, compared to 225/649 (35%) for all screen-detected cancers (P < 0.0001).

CONCLUSION: Most cases met the NLST criteria for a positive screen. Awareness of missed abnormalities and interpretation errors may aid lung cancer identification in CT screening.

KEY POINTS: • Lung cancer within a year of a negative CT screen was rare. • Abnormalities likely due to lung cancer were identified retrospectively in most patients. • Awareness of error types may help identify lung cancer sooner.