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CT Scans or X-Rays? Lung Cancer Screening Trial Raises Some (Ethical) Dilemmas
A massive new study that’s caught the eye of the scientific community and the media alike reports that CT scans significantly cut the risk for lung cancer deaths over x-rays in very heavy smokers. For a disease that kills 85% of its victims within five years(1), and 60% within one year(2), the results may sound like a godsend. And there’s no doubt about it: the study illustrates beautifully the increasing power of medical technology to catch diseases early.
But this finding also comes at a time when there are heated debates about screening recommendations for the public. For instance, two major U.S. organizations are at odds about their recommendations for the appropriate age a woman should begin mammogram screening. And CT scans are being scrutinized for their safety after some patients were recently determined to have received radiation overdoses from the scans.
The new National Lung Screening Trial (NLST), the largest of its kind(3), also raises some important questions about how and when tests should be offered to the public, and how we as a nation decide when and if the benefits of a medical test outweigh the risks — and the costs — of screening.
What the Study Found
In the current study, over 53,000 current and former heavy smokers between the ages of 55 and 74 were randomly assigned to receive either CT scans or x-rays. To be considered heavy smokers, participants had to have racked up 30 pack-years, meaning that they smoked one pack per day for 30 years or two packs per day for 15 years, and so on. Participants were screened with CT or x-ray, depending on which treatment group they were in, once a year for three years. After this, they were followed for five years, with lung cancer frequency and mortality being the key variables that the researchers were interested in tracking.
After the five years of follow-up, people in the CT scan group had a 20% lower mortality rate than people who received x-rays (354 people in the CT group died of lung cancer, vs. 442 in the x-ray group). They also had a 7% lower mortality rate from any cause, but the reason for this finding is still unclear. Since the data for the study still haven’t been released, speculating about the reasons behind all of the findings is somewhat difficult at this time.
Raising Even More Questions Than It Answers
Should all smokers run out and demand helical CT scans from their doctors? The answer is likely "no." For one thing, we still don’t know whether the results of the current study apply to other groups of smokers, including moderate and light smokers and younger smokers.(4) Additionally, there is a fairly high "false-positive" rate with helical CT scans: in the current study, the false-positive rate was 25%, meaning that doctors saw masses (or "nodules") that required further investigation but turned out to be benign, which may have led to unnecessary testing and additional expense.
As you may have noticed by now, the study raises almost as many questions as it answers. For example, how do we determine whether the benefits of a particular screening procedure outweigh its risks? As mentioned earlier, CT scans may expose patients to unsafe levels of radiation if they are done too frequently. As a result, we need to think about where the balance point lies between the dangers of over-screening and the obvious dangers of missing the disease.
Along those lines, should the high false-positive rate found in the current study affect how often CT scans should be recommended to current or former smokers? On the other hand, should these benign nodules actually be considered false-positives, since they still masses that deserve investigation? And, of course, still up in the air is who should decide when and how often screening is recommended: Should it be up to the government or should it be the decisions of the individual doctors themselves? Finally, should the cost of the scans (which are not typically covered by insurance) be a factor in who gets one or not?
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