CT screening for lung cancer: past and ongoing studies

Abstract

It has been widely recognized that the oft-quoted randomized clinical trials (RCTs) of lung cancer screening by chest radiography--studies that were interpreted as showing no benefit--were seriously flawed. We begin by describing the shortcomings of these trials and presenting an analysis of the problems typically encountered in performing RCTs in this area. Screening for lung cancer using computed tomography (CT) has shown that CT offers great superiority over chest radiography in diagnosing small lung cancers in the three studies that performed both CT and chest radiography on all patients. The Early Lung Cancer Action Project (ELCAP), showed that false-positive results can be kept reasonably low and are much less common on repeat screening, and that CT screening can be managed with no notable excess of percutaneous or surgical biopsies when following a well-defined regimen of screening. This regimen details the parameters of the initial CT, the definition of a positive result, and the subsequent work-up of positive results. Following the updated International (I)-ELCAP protocol, it has been further found that (1) the frequency of positive results is low: 15% for the baseline cycle of screening and 6% for the subsequent cycles. (2) The frequency of screen-diagnoses as compared with all diagnoses is 97% or higher. (3) The relative frequency of presurgical Stage I is well over 80%; the median diameter of the screen-diagnosed cases on repeat screening is 8 mm (versus 15 mm at baseline screening). (4) A high percentage of the screen-diagnosed cases were genuine cancers which led to death if not treated. (5) The estimated 8-year cure rate for resected baseline screen-diagnosed lung cancers without evidence of lymph node metastases is 95% and for resected annual repeat cancers is 98%. (6) CT screening appears to be highly cost-effective. These preliminary results of CT screening suggests that the cure rate of screen-diagnosed lung cancer, using the I-ELCAP regimen of screening, may be over 70% as compared with that of usual care of 10% and that of chest radiographic screening of 20%.