For the first time, a screening method has been shown to reduce lung cancer mortality. Preliminary results from the large National Cancer Institute (NCI)-sponsored National Lung Screening Trial (NLST) show a 20% reduction in lung cancer deaths in a high-risk population screened with low-dose helical CT scans versus conventional chest X-ray.
“These results demonstrate the rigorously defined ability of low-dose helical CT scans to reduce deaths from lung cancer in an older, high-risk population of heavy smokers,” stated Harold Varmus, MD, Director of NCI. “But no one should come away from this trial believing that it is safe to continue to smoke. Low-dose helical CT scans do not prevent or protect against lung cancer, and smoking has many other detrimental effects in addition to lung cancer.”
Neither NCI nor study investigators are making any screening recommendations based on the preliminary findings of the NLST. First a thorough analysis of the data will be conducted, followed by publication of full study details in a peer-review journal. After that, recommendations from several groups, such as American Cancer Society, American College of Radiology, and Radiological Society of North America, are expected.
The study enrolled more than 53,000 current and former smokers aged 55 to 74 in August 2002. The study was conducted at 33 centers in the U.S. at a cost of more than $250,000,000. All participants had a history of at least 30 pack-years (i.e., smoked at least a pack a day for 30 years) and were free of signs, symptoms, or a history of lung cancer at enrollment. Participants had three annual screens with either low-dose helical CT scans (also called spiral CT) or standard chest X-ray.
As of October 10, 2010, a total of 354 lung cancer deaths were reported in the spiral CT arm versus 442 in the chest X-ray arm, representing a 20.3% reduction in lung cancer mortality. At that time, an independent Data Safety Monitoring Board review recommended that the study be stopped early due to the obvious benefit of spiral CT screening.
An intriguing finding of the study, which remains to be fully elucidated, was a 7% reduction in all-cause mortality among the group screened with spiral CT versus those in the conventional x-ray group. Potential explanations could include fewer deaths from cancers other than lung, respiratory disease, and cardiovascular disease.
Despite the positive findings of this study, CT screening has some disadvantages that need to be considered. First is cost. A diagnostic low-dose helical CT scan (as opposed to a screening scan) costs about $300, and the screening scan should fall in that ballpark. Insurers, including Medicare and Medicaid, do not reimburse for lung cancer screening, although they do provide reimbursement for diagnostic scans once symptoms of lung cancer appear. A second consideration is the 25% false-positive rate in the CT group necessitating further workups and more medical procedures that can lead to complications. Another concern is whether lifetime radiation exposure from spiral CT increases the risk of cancer.
To put this in context, radiation exposure from spiral CT study amounts to about 1.4 millisieverts (mSv) compared with an average of about .1 mSv for the single-view chest X-ray used in this study. Radiation exposure from a 2-view breast mammogram averages from 2.5 to 3.5 mSv.
One question that will be answered by complete analysis of LCST data is which subgroups, if any, had a preferential benefit from spiral CT. It is also possible that other groups not included in NLST may have a survival advantage from spiral CT, such as younger patients, light smokers, and non-smokers.
“These findings should not be interpreted to mean that the general public should have low-dose helical CT scans. Only high-risk patients were studied. Modeling will be done [based on trial data] to determine who should get them,” stated Douglas R. Lowy, MD, Deputy Director of NCI.
Presumably, the survival benefit of spiral CT is due to detecting lung cancers at an earlier stage when they are treatable. However, that was not the focus of the trial. “We assume that earlier detection accounted for reduced mortality, but this will be subjected to further analysis. The power of this study is that it met the ultimate endpoint—deaths from lung cancer were reduced. It is important to stress that,” stated Dr. Varmus.
– by Alice goodman
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