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Screening for lung cancer with CT scans

Posted By Peter Wehrwein On November 4, 2010 @ 9:25 pm In Cancer | Comments Disabled

Lung cancer is usually discovered late when it’s difficult to treat and has often spread outside the lung. A reliable screening test to find it at an earlier, more treatable stage would be a legitimate breakthrough—and could potentially save thousands of lives. About 160,000 Americans die each year from lung cancer, which is more than who die from breast, prostate, and colon cancer combined.

Chest x-rays do a good job of finding small lung cancers that can be removed surgically. Why not use them to screen for lung cancer? Because at least a half-dozen studies have been done and for reasons that aren’t entirely clear, early detection with chest x-rays hasn’t translated into prevention of fewer deaths from lung cancer. And in screening, early detection is a means to an end. The real goal is preventing deaths from the disease that is being screened for (and deaths in general).

So it was big news today when the National Cancer Institute (NCI) announced today that a large study sponsored by the institute showed that screening current and former heavy smokers with computed tomography (CT) scans did, in fact, reduce the risk of dying from lung cancer by 20% compared with screening them with chest x-rays. Moreover, those who were screened with CT scans were 7% less likely to die from any cause during the study’s five-year follow-up period.

Good news, and a long time coming for those who have watched disappointing findings from the chest x-ray studies pile up.

But if today was first time that most of us heard about the National Lung Screening Trial, it probably wouldn’t be the last. It’s almost certainly going to stir up more than its fair share of controversy.

Here are a few of the hot buttons:

  • The NCI says there are more than 94 million current and former smokers in the United States (mind you, not all of them are heavy smokers, so the population to be screened may be smaller). It will be very expensive to screen them all with CT scans. How much a screening CT of the lung will cost is hard to say, especially if they become routine, but the NCI says the current Medicare reimbursement rate for a diagnostic CT scan of the lung is $300.
  • Some may argue that smokers shouldn’t be entitled to such an expensive test—or should have to shoulder a large share of the cost. The counterargument is why single out smokers when other bad health habits result in expensive tests and treatments.
  • The NCI itself showed that there’s concern that some people may see an effective screening test as a reason to tune out the dire health warnings about tobacco and cigarettes. In a Q&A about the study posted on its Web site today (which is well worth reading if you want more detail about the study), the third question is, “Is it OK to keep smoking because there is a screening test that has benefit?” The answer begins with an emphatic, “No.” It’s hard to imagine that people would actually ask such question, but the NCI apparently was worried enough to pose it.
  • Radiation exposure and the cancer risk from medical imaging (and CT scans in particular) has become a major issue. Will the radiation from CT screening for lung cancers add to the problem? The NCI position: the radiation from a screening CT is far less than the dose from a diagnostic one and that benefit of finding and treating early lung cancer will likely outweigh the risk from a low dose of radiation from CT scanning.
  • In the Q&A about the study, the NCI says that between 20% and 60% of  screening CT scans of current and former smokers show some kind of abnormality and that most are not lung cancer. CT scanning for lung cancer could generate a large number of false positives: results that indicate the possibility of cancer but turn out not to be. False positives result in worry and additional tests, which in the case of lung cancer would include invasive biopsies.

Of course many of our current screening tests for cancer have shortcomings, cost plenty, and are controversial. The debates about the value of mammography never seem to end. Yet we get behind screening tests for a whole variety of reasons, not the least of which is that cancer caught late is so lethal and, these days, astronomically expensive to treat.

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