Study objectives: Low-dose helical CT scanning identifies early stage lung malignancies and also a large proportion of lung nodules of uncertain diagnostic and prognostic significance (ie, indeterminate nodules). The sensitivity, specificity, and predictive value of these indeterminate nodules detected by CT scanning as part of a lung cancer screening program is largely unknown. We therefore calculated the sensitivity, specificity, and predictive values of CT-detected lung nodules that were followed up at least 18 months.
Design: Single-arm screening trial with longitudinal follow-up.
Setting: Rural areas of United States, from 2000 to 2004.
Participants: Former and current nuclear weapons workers, ≥ 45 years old, including smokers and never-smokers, with variable exposure to occupational lung carcinogens.
Interventions: A total of 4,401 participants were CT scanned for lung cancer with an initial full chest low-dose CT scan, interval CT scans at 3, 6, and 12 months for indeterminate lung nodules (eg, nodules not immediately suspicious for lung cancer), and a 18-month, full-chest, low-dose incidence CT scan.
Results: We achieved follow-up for a minimum of 18 months for > 95% of 807 participants with indeterminate or suspicious lung nodules. Only 3 of 727 indeterminate nodules were identified as being malignant during the subsequent 18 months. The radiologist’s designation of a nodule as suspicious had a sensitivity of 84.2% and a specificity of 96.6%. Given a prior probability of lung cancer of 2.4%, positive and negative predictive values were 37.2% and 99.6%. Overall, we detected 33 primary lung cancers, including 19 stage I cancers, 5 stage II cancers, 7 stage III-IV cancers, and 3 limited-stage small cell cancers.
Conclusions: Helical CT scanning detects many indeterminate nodules, but few are malignant. CT scanning has high sensitivity and specificity to detect early lung cancer. The problem of false-positive results in helical CT scanning is limited and can be rationally managed. Current CT follow-up recommendations are supported.