We appreciate the opportunity to respond to Dr. Petty's letter. It is important to correct his misunderstanding regarding the Task Force recommendation (1). The I letter grade is meant to communicate the lack of sufficient evidence to make a recommendation (either for or against screening); it is distinct from the D letter grade, which is a recommendation against screening.

We should screen to detect early-stage lung cancer only if it is shown that, overall, the process of screening—which includes diagnostic work-up and treatment—does more good than harm. The Task Force did not find evidence that this has been established for lung cancer. In the absence of adequate evidence of net benefit, there is the potential that screening could do more harm than good.

Screening for lung cancer causes known harms. Low-dose computed tomography is not a highly specific test: Prevalence rates of false-positive test results range from 5% to 41%, probably because of underlying differences in the patients studied (1). Follow-up on false-positive test results, besides causing unnecessary psychological harm, can lead to unnecessary invasive procedures that can result in physical harm. The morbidity rate from thoracotomy ranges from 9% to 44%, and the mortality rate from invasive procedures in symptomatic persons ranges from 1% to 12% (1).

Furthermore, there is inadequate knowledge of the natural history of early-stage lung cancer and its progression to advanced cancer. The Mayo Lung Project found increased rates of early tumors in screened patients without any change in the numbers of advanced tumors or subsequent mortality rates, indicating that a proportion of early-stage lung cancer may be relatively indolent (2). The overdiagnosis and overtreatment of early-stage lung cancer may cause harm, in ways similar to the overdiagnosis and overtreatment of prostate cancer and breast cancer. The evidence published up to the time of the Task Force review did not clarify whether these harms are a cause for real concern.

The evidence of the efficacy of low-dose computed tomography comes from cohort studies, including those done in Japan. The design of these studies subjected the results to several potential sources of bias. Therefore, the efficacy of low-dose computed tomography screening in reducing lung cancer mortality cannot be definitively evaluated as yet, and no conclusions can be drawn regarding the benefits, the harms, or the balance of these outcomes. At least 3 randomized, controlled trials designed to evaluate the efficacy of lung cancer screening programs in reducing lung cancer mortality are under way. The results of these studies should provide the Task Force with the evidence required to make a recommendation on lung cancer screening.