The I-ELCAP investigators, at 33 institutions throughout the world since 1993, have been performing CT screening for lung cancer to evaluate its usefulness.

Baseline screening has been performed on 26,577 men and women. They have subsequently undergone 19,555 annual repeat screenings. Positive results of the initial CT and their ensuing diagnostic work-up were defined by a common protocol. A lung cancer diagnosis was classified as a baseline screen-diagnosis if the work-up was prompted by a positive finding on the initial CT and as an interim-diagnosis in the baseline cycle if it was prompted by symptoms emerging prior to the first repeat screening 12 months later. Analogous attributions were applied in the repeat cycles. Kaplan-Meier analysis was applied to resected cases to determine the lung cancer case-fatality.

The initial CT was positive in 15% and 6% on baseline and repeat screenings, respectively. Of a total of 317 diagnoses of lung cancer in the baseline cycle, 313 (98%) were screen-diagnoses. In the repeat cycles, 63 (98%) of 64 were screen-diagnoses. Among the 376 (313+63) screen-diagnosed lung cancers, 82% were of Stage I. Of the 376, 303 were resected, and the 8-year lung cancer case-fatality rate was 4%.

Annual CT screening produces a high percentage of Stage I diagnoses of lung cancer, and lung-cancer mortality is very low after resection.