Spiral CT Screening Shown to Result in Lower Lung Cancer Deaths

New findings revealed that 20% fewer lung cancer deaths were seen among those who were screened with low-dose spiral computed tomography (CT) than with chest X-ray.

The US National Cancer Institute (NCI; Bethesda, MD, USA) released initial results from a large-scale test of screening methods to reduce deaths from lung cancer by detecting cancers at relatively early stages.

The National Lung Screening Trial (NLST), a randomized US trial involving more than 53,000 current and former heavy smokers ages 55 to 74, compared the effects of two screening procedures for lung cancer--low-dose helical CT and conventional chest X-ray--on lung cancer mortality and found 20% fewer lung cancer deaths among trial participants screened with low-dose helical CT. The NLST was sponsored by NCI, a part of the National Institutes of Health, and conducted by the American College of Radiology Imaging Network (ACRIN; Reston, VA, USA) and the Lung Screening Study group. The study was published November 3, 2010, in the journal Radiology and is available online.

Starting in August 2002, the NLST enrolled about 53,500 men and women at 33 trial sites nationwide over a 20-month period. Participants were required to have a smoking history of at least 30 pack-years and were either current or former smokers without signs, symptoms, or history of lung cancer. Pack-years are calculated by multiplying the average number of packs of cigarettes smoked per day by the number of years a person has smoked.

Participants were randomly assigned to receive three annual screens with either low-dose helical CT (frequently referred to as spiral CT) or standard chest X-ray. Helical CT uses X-rays to obtain a multiple-image scan of the entire chest during a 7 to 15 second breath-hold. A conventional chest X-ray requires only a subsecond breath-hold but produces a single image of the whole chest in which anatomic structures overlie one another. Previous efforts to demonstrate that standard chest X-ray examinations can reduce lung cancer mortality have been unsuccessful.

The trial participants received their screening tests at enrollment and at the end of their first and second years on the trial. The participants were then followed for up to another five years; all deaths were documented, with special attention given to the verification of lung cancer as a cause of death. At the time the DSMB held its final meeting on October 20, 2010, 354 deaths from lung cancer had occurred among participants in the CT arm of the study, whereas a significantly larger 442 lung cancer deaths had occurred among those in the chest X-ray group. The DSMB concluded that this 20.3% reduction in lung cancer mortality met the standard for statistical significance and recommended ending the study.

An ancillary finding, which was not the main endpoint of the trial's design, demonstrated that all-cause mortality (deaths due to any factor, including lung cancer) was 7% lower in those screened with low-dose helical CT than in those screened with chest X-ray. Approximately 25% of deaths in the NLST were due to lung cancer, while other deaths were due to factors such as cardiovascular disease. Additional analysis will be required to understand this facet of the findings more fully, according to the investigators.

The possible disadvantages of helical CT include the cumulative effects of radiation from multiple CT scans; surgical and medical complications in patients who prove not to have lung cancer but who need additional testing to make that determination; and risks from additional diagnostic work-up for findings unrelated to potential lung cancer, such as liver or kidney disease. Moreover, the screening process itself can generate suspicious findings that turn out not to be cancer in the vast majority of cases, producing significant anxiety and expense. These difficulties should be weighed against the advantage of a significant reduction in lung cancer mortality.

It should also be noted that the population enrolled in this study, while ethnically representative of the high-risk US population of smokers, was a highly motivated and primarily urban group that was screened at major medical centers, according to the investigators. Therefore, the results may not precisely predict the effects of recommending low-dose helical CT scanning for other populations.

Related Links:
National Cancer Institute
American College of Radiology Imaging Network