Since the introduction of spiral computed tomography (CT) scanning in the 1990s, researchers and physicians have been hopeful that the imaging tool would be helpful in detecting early, localized lung cancers that could be successfully treated. Uncontrolled studies showing that spiral CT can detect small-sized lung cancers have nurtured this hope, but the clinical significance of the findings of these studies remains unclear.
Despite a lack of evidence about whether spiral (also called helical) CT screening for lung cancer saves lives, direct-to-consumer marketing has increased demand for the procedure. However, the results of a recent study that used a computer-simulated model of 100,000 current, quitting, and former smokers older than age 60 suggest that screening for lung cancer with spiral CT scanning may not be cost-effective. CT scanning is readily available at commercial facilities or even in a hospital setting, and patients who opt for the procedure can pay to have either a whole-body scan or perhaps a spiral CT scan for lung cancer specifically.
"Right now based on the current available data, we are saying that direct-to-consumer marketing [of spiral CT scanning] is not advisable," said Parthiv J. Mahadevia, M.D., a co-author of the study that appeared in the January 15 issue of the Journal of the American Medical Association. "It is not advisable because the benefit of screening is still unknown and because there is a possibility of harm. We urge restraint in marketing until the benefit is clearly established. However, CT screening is promising and deserves further study," said Mahadevia, who is a research scientist at MEDTAP International, Bethesda, Md. Mahadevia was at Johns Hopkins University School of Medicine, Baltimore, when the study was conducted.
Mahadevia and colleagues used a hypothetical cohort of current, quitting, and former smokers who were screened annually from age 60 to age 80. The analyzed data represented 462,352 screenings over 20 years and were compiled from studies of lung cancer and from the Surveillance, Epidemiology, and End Results (SEER) cancer database.
Cost Estimates
The estimated cost of screening current smokers was $116,300 for each quality-adjusted life-year (QALY) gained. For people who quit smoking when they were first screened, the cost was $558,600 per QALY and $2.3 million per QALY for former smokers.
"If you started screening the entire male population over the age of 50, it would be astronomically expensive," said Victor R. Grann, M.D., co-author of an editorial that accompanied Mahadevias study. "Giving flu shots to the same population would probably save many more life years." Grann is clinical professor of medicine and public health at Columbia University College of Physicians and Surgeons, New York.
Using their model, the authors calculated that there would be fewer deaths among people who were screened; there would be 3,615 deaths attributed to lung cancer per 100,000 people in the screened group, compared with 4,168 deaths in the group that was not screened. Although this represents a decrease of 13% (553 deaths) in the screened group, screening also resulted in 1,186 invasive tests or surgeries for benign lesions.
The high potential for false-positives, combined with the societal cost of the scan and follow-up procedures, warrant caution in direct-to-consumer marketing of spiral CT scanning until the benefits of the scan are proven, Mahadevia and colleagues concluded.
"We are not preventing anyone from getting this test, only advising them that the supporting evidence for benefit has not been established," he said. "Individuals should consider the fact that there is a possibility of having to get more tests, and paying for those tests, if the insurance company balks at covering them."
He added that people who are considering having a scan must weigh several factors, including the possibility that additional scans, tests, surgery, chemotherapy, or radiation may be needed. Mahadevia said that patients should be given full informed consent regarding the procedure.
National Lung Screening Trial
To determine whether screening for lung cancer reduces the number of deaths from the disease, the National Cancer Institute launched the National Lung Screening Trial (NLST) in September 2002. To date, the trial has enrolled 29 active sites nationwide and recruited more than 16,000 current or former smokers. It is expected that recruitment of 50,000 people will be completed by July 2004.
The goal of this randomized, controlled trial is to determine whether screening for lung cancer using spiral CT compared with chest X-ray can reduce mortality from lung cancer and to compare the benefits to the harms. "In order to do that you need a study designed with the kind of numbers and power and logistics to recruit 50,000 people, which is the safe outlying number to look at," said Jonathan Goldin, M.D., Ph.D., of the University of California at Los Angeles and a co-principal investigator of the American College of Radiology Investigational Network (ACRIN), which is one of the two research networks coordinating the trial. (The other is the network that has been coordinating the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial.) "Statistics is a numbers game, and the best and safest numbers come from having solid data that reflect population statistics. That doesnt come cheap or easy."
Although the work of the NLST may not be completed until 2009, there will be interim analyses. The first report detailing recruitment and incidence data are expected at the end of 2004.
The two most serious downsides of screening for lung cancer are false-positives, which are caused by the detection of benign lesions that appear malignant, and overdiagnosis, or "pseudodisease."
"Pseudodisease is a real phenomenon, and there is a lot of confusion surrounding it," said William Black, M.D., professor of radiology and community and family medicine in the Department of Radiology at Dartmouth-Hitchcock Medical Center, Lebanon, N.H. Black defines psuedodisease and overdiagnosis as a "diagnosis of a condition that would not have become clinically significant had it not been detected through screening."
The most frequent form of overdiagnosis occurs in the case of a lesion only a few millimeters in diameter that may be diagnosed as cancer but may never cause a clinical problem. "Many of these lesions remain dormant for 10 or 20 years, and only a small fraction of them will explode into a clinically significant cancer," Black explained. "If you looked at them under a microscope, they would be called cancer, but the person who had it never would have been affected by it."
Because smokers are at risk of developing other diseases as they age, the person may die of a competing cause before the lesion would cause any problem to the patient.
False Feedback
Overdiagnosis not only causes patients to undergo additional testing and the concomitant stress but also drastically skews statistics. "It gives all sorts of false feedback in term of false-positive rate and greatly distorts survival statistics because you are putting people in your survival group that didnt even have [life-threatening] cancer," said Black. "It has a dramatic effect on 5-year survival and cure rates."
But because the NLST will not be completed for years, the question arises: what should patients and their physicians do in the interim?
Goldin recommends that they join the NLST. Patients enrolled in the trial will receive the tests free of charge, will be informed about the possible risks of screening for lung cancer, and will be put on a standard protocol that is used for all patients, which includes annual testing for 3 years.
Smokers who opt for screening outside of a clinical trial may have misconceptions of what to expect from a screening CT. "People think that it (a spiral CT scan) is another test like a blood test," Goldin explained. "But screening with imaging is not a diagnostic test like a blood test. It is a whole clinical evaluation. We need to work out three things in my opinion: Does the test work? How do you do the test optimally? How do you manage the patients once you have tested them?"
Mahadevia expressed similar concern, pointing out that, for now, CT scanning may be most useful for diagnosing a condition in patients with specific symptoms.
"Its a very different scenario if someone comes in with fever, weight loss, and is coughing up blood," Mahadevia said. "It is imperative to find the cause of these symptoms. Thats a very different clinical context than screening people who do not have any good clinical indication for a test. Mass screening of the populace can lead to many incidental findings, which are of unclear clinical significance. What do these findings mean to the patient? You dont know if it is a problem or not."
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