Lung cancer is the leading cause of cancer deaths. As with most cancers early discovery may be a key factor in decreasing mortality and improving long-term survival. The earlier the cancer is found the more likely the treatment will be able to stop or delay the spread of cancer or prevent extensive local damage. Unfortunately, outward signs of lung cancer may not develop until it is in later stages. An effective screening program to find lung cancer in its early stages may help reduce mortality rates or increase the length of survival. Because of the strong link between smoking and lung cancer many lung cancer-screening programs focus on people with long history of smoking.
Researchers on the National Lung Screening Research Team investigated if a low-dose computed tomography (CT) scan could effectively screen for lung cancer in long-term smokers. A CT scan is type of x-ray that can take cross-sectional images of the inside of the body. The scan can make clearer images of organs than standard x-rays. The study, published in New England Journal of Medicine, found that screening with the CT scan decreased the rate of death overall and the rate of death due to lung cancer compared to screening with a standard chest x-ray.
The randomized trial included 53,454 patients between ages 55-74 years with at least a 30-pack year history of smoking. Pack years is a tool physicians use to estimate lifetime exposure to tobacco. It takes into account number of cigarettes smoked per day and the number of years of smoking. The pack year history in this trial is considered a high risk for the development of lung cancer. The participants were randomized to three annual screenings with either low-dose CT scan or single view chest x-ray. They were followed for 6.5 years for the development of lung cancer and death. About 93%-95% of participants in both groups completed all three screenings.
Results from scans include
- abnormalities (positive screen) found in initial screen in 27.3% with CT scan vs. 9.2% with x-ray
- positive screens over all 3 rounds in 24.2% with CT scan vs. 6.9% with x-ray
- false positive (scan indicated something when there was nothing) rate 96.4% with CT scan vs. 94.5% with x-ray
- lung cancer diagnosed in 1,060 patients with CT scan vs. 941 patients with x-ray
Despite the higher incidence of diagnosed cancers, CT scans were associated with lower rates of death from lung cancer and death overall:
- lung cancer deaths occurred in 1.33% of patients with CT scan vs. 1.66% of patients with x-ray (statistically significant difference)
- death from any cause occurred in 7.02% of patients with CT scan vs. 7.48% of patients with x-ray (statistically significant difference)
The trial was stopped early because the CT scan was found to be significantly better during an interim analysis.
Large randomized trials are generally considered a very reliable form of research. More trials will be done to assess the benefits and risks of lung cancer screening but CT scan appears to be a more reliable form of screening than plain chest x-ray in high-risk patients. The benefits found in this trial can only be applied to the types of participants in this trial, high-risk smokers aged 55-74 years. Earlier trials assessing chest x-rays found that frequent chest x-rays were not associated with decreased mortality. Since the CT scan was compared to chest x-rays it may have overestimated the benefits of CT scans. Further trials comparing to other screening methods will help clarify CT scan benefits.
Although there is still some research to be done, the CT scan appears to be an effective screening option for people at high-risk. The CT scan in general has been used for several health issues and is generally considered safe despite some radiation exposure. The American Lung Association adjusted their screening guidelines based on this trial. The advisory suggests that people aged 55-74 years with at least 30 pack-year smoking history can undergo low-dose CT scanning to help detect lung cancer early.
If you fit into this group, discuss the risks and benefits of screening with your doctor.
The National Lung Screening Trial Research Team. Reduced Lung-Cancer Mortality with Low-Dose Computed Tomographic Screening. N Engl J Med 2011; 365:395
American Lung Association. ALA Provides Guidance on Lung Cancer Screening. Available at: . Accessed May 8, 2012.
Last reviewed May 2012 by Brian P. Randall, MD
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