Not everyone should get screened for lung cancer using CT scans.

Health and medicine explained.
Nov. 15 2010 4:09 PM

CT Scam

Don't believe the hype about lung-cancer screenings.

CT medical scanner.
A CT medical scanner.

November is Lung Cancer Awareness month. In Atlanta this week you may have heard a dulcet-voiced doctor on the radio announcing that "anybody can develop lung cancer," and the alarming factoid that women who have never smoked are the fastest-growing segment of people getting the diagnosis. In California, a press release announced that anyone who has smoked for more than 10 years is a "patient at risk" for lung cancer, and another advised that "prior smokers over 50 years of age"would benefit from screening.

But these are not public-service announcements intended to raise awareness of the No. 1 cancer-killer. They are advertisements promoting computed tomography lung cancer screening from St. Joseph's Hospital in Atlanta, Wilshire Radiology Associates in Beverly Hills, Calif., and the Bonnie Addario Lung Cancer Foundation (which sponsors a CT screening program at Sequoia Hospital in Redwood City, Calif.). There are more examples, too—coming from hospital Web sites and physicians' groups. And they are all dangerously misleading.

On Nov. 4, the National Cancer Institute held a press conference announcing that a large randomized trial of CT screening had shown an astounding 20 percent reduction in the risk of death from lung cancer among participants. This is a huge step forward in lung-cancer prevention, no doubt. But the Institute said little about who should be screened, or the risks that are involved.

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They should have. Cancer screening is fundamentally inefficient: Hundreds, and sometimes thousands, of people must be screened to help just one or two. Each person who undergoes the test may suffer consequences from it, even though most will never get any counterbalancing benefit. This is why the recent study—called the National Lung Screening Trial—focused on a narrow, "high-risk" subgroup of the adult population who ranged from 55 to 74 years old and had smoked at least a pack a day for 30 years. If they had quit, it was within the past 15 years.

These are strict criteria, and they ensured that the patients had a meaningful chance of developing lung cancer during the course of the decadelong study—and thus an opportunity to benefit from being screened. But people who are younger or have smoked less than the test subjects are at much lower risk for the disease (although no one is entirely safe from it).

If you have a lower risk of lung cancer, there's less of a chance that screening will help you, as you can't prevent something that wasn't going to happen. But that doesn't mean there's less of a chance you'll be harmed by the procedure. Taking a CT scan of the chest can uncover something that looks abnormal but ends up being nothing. Along the way there are more scans, biopsies and, sometimes, unnecessary surgeries. In the NCI study one in four people had these false positives. A prior study from the University of Pittsburgh pegged the rate at around two out of five, and in that study one in 100 subjects had parts of their lung removed for no good reason.

CT screening can also uncover small lung cancers that you'd be better off not knowing about, because they would be unlikely to progress and make you sick. This problem of overdiagnosis is familiar in prostate cancer—many cancers found by the PSA test are not dangerous. A study from 2007 showed that CT screening may uncover one overdiagnosed cancer for each real cancer it turns up. The NCI has not yet released the equivalent numbers from its new trial, but the data we do have suggest that the ratio is about the same—about one in 70 patients is told he has lung cancer when the condition might end up being harmless.

Leaving aside false positives and overdiagnoses, screening is not a panacea. Not even close. The NCI study showed that regular scans prevented one in five lung cancer deaths, which means that four out of five sneaked through. It's amazing to save even one in five people, but it also means that the number who benefit from screening is a lot smaller than the number who test positive. All told, a death from lung cancer was prevented in one out of every 300 people in the study.

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