It seems logical—and appealing—that early diagnosis of lung cancer is beneficial. But simple logic can be misleading when interpreting studies on cancer screening. The central issue is that the longer survival of patients with screen detected cancers results from a combination of lead time bias, length bias, overdiagnosis bias, and true effectiveness of screening.1

By design, screening detects cancers earlier (lead time), but earlier detection may not change the time until death from cancer. Periodic screening will detect a large proportion of slower growing cancers because they persist longer in an asymptomatic state (length bias), and it may detect slow growing cancers that do not need treating (overdiagnosis). Without a control group, it is difficult if not impossible to distinguish between these effects, or even to be sure that screening has any true effect at all.

Despite this, early detection promises the best hope for reducing mortality due to lung cancer. The recently published results of the International Early Lung Cancer Action Program …