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CT Screening for Lung Cancer: Not Ready for Routine Practice¹

¹ From the Department of Radiology, Duke University Medical Center, Box 3808, Durham, NC 27710 (E.F.P., P.C.G.); and the Department of Radiology, Dartmouth-Hitchcock Medical Center, Lebanon, NH (W.C.B.). Received October 12, 2000; revision requested October 24; revision received November 21; accepted December 9. Address correspondence to E.F.P. (e-mail: patz0002@mc.duke.edu).

View larger version (42K): [in a new window]   Figure 1. Schematic illustrates lead-time bias. Considering two comparable cases of lung cancer, the case in the screened group is diagnosed earlier than the case in the control group. Therefore, the screening-detected case must survive longer from the time of diagnosis, even if death is not delayed by earlier detection. Note that both patients develop metastatic disease (indicated by symbols over the lower extremities).

View larger version (34K): [in a new window]   Figure 2. Schematic illustrates length-time bias. Rapidly growing tumors have a short potential screening period (interval between detection and symptoms), while more indolent (slowly growing) tumors have a longer detectable preclinical phase. Therefore, cases detected at screening tend to progress more slowly than those that are not detected at screening and manifest clinically. Consequently, screening-detected cases tend to progress less rapidly than interval cases. Tumor onset is shown in the "patient" on the left, detectable tumor is shown in the middle, and symptomatic tumor is shown on the right.

View larger version (43K): [in a new window]   Figure 3. Schematic illustrates overdiagnosis bias. Consider two screening-detected cases of lung cancer (top) and two comparable cases in the control group (bottom). Only one of the two cases in the control group is diagnosed because the other one remains asymptomatic until the patient dies of causes other than lung cancer. In this example, lung cancer survival is 50% (one of two survives) in the screened group but 0% (the one patient with a diagnosis) in control group, although in each group only one patient dies of lung cancer (ie, mortality is the same). Note that in the control group, one patient dies with undiagnosed lung cancer, which did not affect the individual’s natural lifespan. An indolent cancer is designated by a black circle, while an aggressive cancer is designated by a "sun" symbol.