Lung cancer continues to be by far the leading cause of cancer deaths, primarily because it is usually not found until it is in a relatively advanced stage. As a result, a great deal of effort has focused on using CT imaging to screen a broad population. The two most influential papers on CT screening for lung cancer published recently have drawn conclusions that are diametrically opposed.1 2 Henschke et al1 found compelling evidence that CT screening would save many patients from death, while Bach et al2 concluded that CT screening may lead to harm through overtreatment of inconsequential lung cancers. It is worth taking a closer look at how two thoughtful groups can arrive at such disparate views.

The paper by Henschke et al1 reported a 5-year survival rate of 86% for patients with lung cancer detected by CT screening. This is dramatically better than the 5-year survival rate of 16% for patients with lung cancer detected by routine care and reported through the US national cancer database.3 The implication is that CT screening has changed the outcome of the patients by early detection and early initiation of treatment.

The paper by Bach et al2 compared the results of three single-arm CT screening studies with predicted results using a model derived from and validated in patients with lung cancer detected during routine care as it exists currently. The number of lung …