November 22, 2010

CT Screening Significantly Reduces Lung Cancer Mortality

CT scan of a human lung

A low-dose CT scan can detect lung cancers at relatively early stages and reduce deaths from lung cancer by as much as 20%, according to a new study. The trial was halted early because of the positive results.

Lung cancer, which is mostly caused by cigarette smoking, is the leading cause of cancer-related deaths in the United States. The majority of cases aren’t detected until symptoms appear. By then, in up to 30% of patients, the disease has spread outside the lungs and is much more difficult to treat.

Researchers have been working to develop methods for identifying lung cancer before symptoms appear. Standard chest X-rays, which produce a single image of the entire chest, can detect tumors greater than 1 cm in size. But there's no evidence that standard chest X-ray exams can reduce lung cancer mortality.

Low-dose helical computed tomography (LDCT)—also called spiral CT—uses X-rays to capture multiple images on a computer. It can detect tumors significantly under 1 cm in size, but studies haven’t yet shown whether LDCT screening can reduce lung cancer death rates. The National Lung Screening Trial, funded by NIH’s National Cancer Institute (NCI), set out to compare LDCT with standard chest X-rays in people at high risk for developing lung cancer. The study design and protocol were described in the online edition of Radiology on November 2, 2010.

Researchers at 33 trial sites nationwide enrolled over 53,000 current or former smokers without signs, symptoms or a history of lung cancer. The participants were randomly assigned to receive 3 annual screens with either LDCT or a standard chest X-ray. They were then followed for up to another 5 years. All deaths were documented, with special attention given to the verification of lung cancer as a cause of death.

On October 20, 2010, the study’s independent Data and Safety Monitoring Board voted unanimously to stop the trial. By that time, there were 354 deaths from lung cancer in the LDCT arm of the study, compared to a significantly larger 442 lung cancer deaths in the chest X-ray group. The Board concluded that this 20.3% reduction in lung cancer mortality met the standard for statistical significance. They also found no evidence of unforeseen side effects.

"This is the first time that we have seen clear evidence of a significant reduction in lung cancer mortality with a screening test in a randomized controlled trial. The fact that low-dose helical CT provides a decided benefit is a result that will have implications for the screening and management of lung cancer for many years to come," says Dr. Christine Berg, the NCI project officer for the study.

The researchers also found that all-cause mortality—death due to any factor, including lung cancer—was 7% lower in the LDCT group. Over half of this difference came from a decrease in lung cancer deaths. The researchers will need to analyze the data further to better understand this and other aspects of the findings.

While NCI has posted the preliminary results online, a fuller analysis with more detailed results will be prepared for publication in a peer-reviewed journal within the next few months.

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