Writing on behalf of the I-ELCAP Investigators. The goal of CT screening is to maximize lung cancer cure rates by early diagnosis and treatment of lung cancer. To achieve this, a regimen of screening is important, particularly for small nodules. To better understand the importance of a regimen, we compared two large databases of screen-diagnosed lung cancers, the International Early Lung Cancer Action Program (I-ELCAP) and the National Lung Screening Trial (NLST) CT arm as the former had a specified diagnostic workup algorithm while the latter did not mandate any specific approach.

We compared all lung cancers including small-cell and carcinoids, that were diagnosed under screening, that is, either screen-diagnosed because of a positive result of the CT screening or symptom-prompted after a negative CT screening. We compared the stage and size distribution of the screen-diagnosed cancers in the International Early Lung Cancer Action Program (I-ELCAP) from 1993 to 2011 and those in the NLST-CT arm from 2002 to 2006. In I-ELCAP, the screenings were performed according to a common protocol in which the diagnostic workup for a participant was defined by a specified protocol which has been continually updated whereas in the NLST, “… no specific diagnostic evaluation approach was mandated.”

In I-ELCAP, a total of 799 patients were diagnosed under screening of which 11 (1.4%) were interim-diagnoses; 8 prior to the first annual repeat screening and 3 between annual rounds, leaving 788 screen-diagnosed patients.

In the NLST CT arm, 1060 patients were diagnosed with lung cancer, but only 692 were diagnosed under screening. There were 18 interim-diagnosed cases before the first annual repeat screening and 26 between the 2 annual repeat screenings, a total of 44 (6.4%) interim-diagnosed cases for this cohort. This left 649 screen-diagnosed patients.

The frequency of clinical Stage I was 82% (95% CI: 79%-84%) vs. 69% (95% CI: 65%-72%) in I-ELCAP and NLST, respectively. Average tumor size (95% confidence interval) was 17.3 mm (16.6-18.1) vs. 23.1 mm (21.7 -24.4), respectively. Surgical resection was performed in 86% (676/788) and 77% (497/649) of the screen-diagnosed patients, respectively. The frequency of pathologic Stage I (clinical, if not resected) was 73% (95% CI: 70%-76%) vs. 63% (95% CI: 59%-67%).

Stage I disease, both clinical and pathologic, was significantly higher in I-ELCAP than NLST. The tumor size was significantly lower in I-ELCAP than NLST, all strongly suggestive of the importance of a specified regimen of screening. This is further substantiated by the reported 71% for pathologic Stage I (clinical, if not resected) by the NELSON study which is close to that reported by I-ELCAP as the NELSON also followed a well-defined regimen of screening.