Worried About Your Lung Cancer Risk? Why a Chest CT Scan May Not Be Wise

Though powerful, chest CT scans have downsides.

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Lung cancer is the leading cause of cancer death in the U.S. and claimed more than 150,000 lives last year. Since most lung cancers are triggered by tobacco use, the best way for family doctors like me to prevent lung cancer in 2011 is to counsel patients not to smoke, or if they already smoke, to quit. Unfortunately, tobacco-damaged lungs often don't heal completely, and ex-smokers continue to be at higher risk for lung and other cancers than never-smokers are.

That's why doctors used to routinely advise that heavy smokers get chest X-rays in hopes of catching cancers at more treatable stages. However, several studies have since found no difference in lung cancer death rates among smokers who got annual chest X-rays versus those who did not. That's likely because the disease is far too advanced to cure by the time it's visible on a chest X-ray.

Computed tomography (CT scans) of the chest, on the other hand, are much more powerful and can detect even smaller lung cancers than X-rays can. Does that mean those cancers will be more curable? To answer this question, several years ago researchers at the National Cancer Institute randomly assigned current and former heavy smokers between the ages of 55 and 74 to annual screening with CT scans or chest X-rays. Last November, they stopped the study early due to evidence showing that patients assigned to receive CT scans had a 20 percent lower risk of dying from lung cancer than those who got chest X-rays. Still, many cancer experts cautioned that these were preliminary results, and that until all of the data from the study are analyzed and published in a peer-reviewed medical journal, patients should not rush to their doctors to request CT scans.

But for the sake of argument, let's say that in the coming months the study's initial results are confirmed, and that screening heavy smokers or ex-smokers for lung cancer with CT scans does, in fact, reduce lung cancer deaths. And let's say that you're worried about your risk, so you visit your family doctor to discuss whether it makes sense to undergo this test. Because most health professionals believe cancer screening saves lives, they may unintentionally minimize, or neglect to discuss, a test's downsides. Screening tests have risks just like any other medical procedure, and it's important for your doctor to thoroughly review those risks with you. Here are 4 good reasons to consider not getting a chest CT scan:

1. The risk of developing cancer from the CT scan itself isn't trivial. A recent analysis published in the Archives of Internal Medicine found that a single chest CT scan exposed patients to the radiation equivalent of more than 100 chest X-rays, and that by age 60, an estimated 1 in 1000 women or 1 in 2000 men would eventually develop cancer from that single scan. (Participants in the lung cancer screening study actually underwent three consecutive annual CT scans.)

2. False alarms are extremely common. In the NCI's lung cancer screening study, researchers found that 1 in 3 patients had at least one false-positive result after undergoing two CT scans. Of those patients, 1 in 14 needed an invasive lung biopsy to be sure they were cancer-free.

3. Even if screening catches lung cancer early, there's no guarantee your prognosis will be better. This is due to "overdiagnosis," or the unnecessary diagnosis of a condition (typically cancer) that will never cause symptoms in a patient's lifetime, either because it's so slow-growing or the patient dies from some other cause. An estimated 1 in 3 breast cancers detected by mammograms is overdiagnosed, and a 2007 study published in the journal Radiology suggested that the proportion of lung cancers overdiagnosed by CT scans could be as high or higher, especially in women. But because there's no way of knowing at the time of diagnosis if a lung cancer will be fatal, inevitably many patients will be needlessly subjected to the side effects of treatment.

4. Finally, it's highly likely that a CT scan for lung cancer will find some other abnormality that will require further investigation. You might think this is a good thing, but studies show that most of these abnormalities turn out to be false alarms, too. In fact, in 2008 the federally-supported U.S. Preventive Services Task Force decided against endorsing CT screening for colorectal cancer due to concerns that investigating all the abnormalities that CT scans turn up could outweigh the cancer-prevention benefits. You may still decide it's worth it for you or a loved one to get a CT scan for the relatively small (about 1 in 300) chance it will prevent death from lung cancer. But before you do, be sure you have all the facts.