CT Lung Cancer Screening Saves Lives, But at What Cost?

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There are only a few cancer diagnoses more terrifying than lung cancer. The disease is responsible for about one-third of all U.S. cancer deaths every year and only 15% of people diagnosed with it live more than five years. These daunting statistics are why U.S. medical professionals have been trying since the 1960s to come up with a way to detect lung cancer at earlier, more curable stages. They may have finally found a way.

A paper documenting the results of the government-funded National Lung Screening Trial (NLST) on the effectiveness of lung cancer screening via computer tomography (CT) was published June 29 in the New England Journal of Medicine (NEJM). It showed that, compared with those screened for lung cancer with regular X-ray, those screened with CT had a 20% lower lung cancer mortality rate. This figured was so significant that when researchers revealed it in late 2010, the trial was stopped early and preliminary results released ahead of time. The paper just published delves into the results more deeply to reveal promising signs, but also warnings that policy makers should proceed with caution before recommending widespread use of this screening tool.

The NLST included more than 53,000 people ages 55 to 74 with an elevated risk of developing lung cancer. To be included in the trial, participants had to smoke or have smoked at least a pack of cigarettes every day for 30 years, or the equivalent. (Someone who smoked, for example, two packs a day for 15 years could also qualify.) Each participant was randomly assigned to receive an annual screening test using either X-ray or CT. In addition to showing a lung cancer mortality rate 20% lower than that of the group assigned to undergo screening via chest X-ray, participants in the CT group also had a 7% lower overall mortality rate.

It may be tempting for some patients and doctors to take the results of the NLST as a sign that every American — or at least every smoker or ex-smoker — should undergo a CT scan to test for the disease. But cancer screening is a complicated science and many factors besides a reduced mortality rate should come into play.

MORE: The Screening Dilemma

First, the expense of screening even only heavy smokers and ex-smokers could be cost prohibitive. In addition to the frontline cost of the CTs themselves, massive expenses would be incurred following up on all the lung abnormalities detected. About one-quarter of trial participants assigned to the CT scan group received a positive screening result indicating possible cancer. Of these more than 90% turned out not to have cancer. The authors of the NEJM study write that the cost of using CT to screen for lung cancer must be weighed against the cost of convincing patients to quit smoking. Medical dollars may save more lives if spent on the latter. There are more than 90 million smokers and ex-smokers in the U.S., meaning the potential population that could be helped by CT is huge, but also that reducing those ranks of over time could significantly cut the number of Americans diagnosed with and killed by lung cancer.

Second, the randomized trial did not examine the health risks of undergoing annual CT scans and the resulting accumulated radiation exposure. The CT screening tests performed for the trial were done at carefully selected sites with highly trained medical personnel, many of whom specialized in radiography. The authors of the NEJM study acknowledged that such expertise may not exist at “community facilities” if the protocol were extended nationwide. The authors also conceded that some CT machines may be more technologically advanced than those used in the trial, meaning they would detect more false positives and result in medical interventions for patients not actually at risk of dying of lung cancer.

Despite these caveats, there’s no doubt that using CT to screen for lung cancer has great promise. The tool may even become a standard practice covered by Medicare and private insurance if researchers are able to further narrow who could be helped by the testing. (Even the more effective CT screen missed plenty of lung cancer during the trial.) Better targeting of the screening test could make the procedure affordable and even more effective.

For now, however, the authors of the landmark study write in the NEJM:

“Although some agencies and organizations are contemplating the establishment of lung-cancer screening recommendations on the basis of the findings of the NLST, the current NLST data alone are, in our opinion, insufficient to fully inform such important decisions.”