CTs Reduce Lung Cancer Mortality
Study Results Raise As Many Questions As Answers
November 8, 2010 | Dagny Stuart
A new study released by the National Cancer Institute (NCI) found that there were 20 percent fewer lung cancer deaths among heavy smokers who were screened with low-dose spiral CT compared with chest X-rays.
The National Lung Screening Trial (NLST) was a nationwide trial of current and former heavy smokers ages 55 to 74. Starting in August 2002, the NLST enrolled about 53,500 men and women at 33 trial sites nationwide over a 20 month period. Vanderbilt-Ingram Cancer Center (VICC) was one of the participating sites and enrolled 465 subjects. John Worrell, M.D., professor of Radiology and Radiological Sciences, was principal investigator for VICC.
Participants were required to have a smoking history of at least 30 pack-years and were either current or former smokers without symptoms or a 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 (often referred to as spiral CT) or standard chest X-ray. Spiral CT uses X-rays to obtain a multiple-image scan of the entire chest. A standard chest X-ray 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. Participants were 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. As of October 20, 2010, a total of 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. Researchers concluded that this 20.3 percent reduction in lung cancer mortality met the standard for statistical significance and recommended ending the study.
“These study results finally give us a clear answer about the benefits of using spiral CT for lung cancer screening,” said Worrell. “We still have not determined how often the screening tests should be done for optimal results and the costs associated with this level of screening.”
Worrell noted that smoking remains the most important risk factor for lung cancer and screening will not reduce the incidence of lung cancer which kills approximately 160,000 Americans every year.
The possible disadvantages of spiral 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. In addition, 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 problems must, of course, be weighed against the advantage of a significant reduction in lung cancer mortality.
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) and the Lung Screening Study group. Read a paper describing the design and protocol of the NLST, “The National Lung Screening Trial: Overview and Study Design” by the NLST research team, published by the journal Radiology.
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