Lung Scan: CT may catch some treatable cancers
A controversial study suggests that computed tomography (CT) scans catch lung cancer early in smokers and other high-risk people, enabling doctors to intervene when they still can improve a patient’s chances of survival. However, some scientists criticize the study’s design for leaving many questions unanswered.
By the time lung cancer is typically discovered, it has spread to lymph nodes or other organs. As a result, only 15 percent of people with lung cancer survive 5 years after their diagnosis. CT scans have been proposed as a tool to find early lung cancers.
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For the new study, which began in 1993, scientists did CT scans of about 31,000 generally healthy people and gave follow-up scans to more than 27,000 of them within 18 months. The participants, who were average age 61, were all smokers, ex-smokers, or people exposed to secondhand smoke or some other lung hazard, such as asbestos or radon.
In the two screenings, or in the interim, 484 participants were diagnosed with lung cancer. Of these, 412 had early-stage cancer confined to the lung. Most underwent surgery promptly after diagnosis.
As of May 2006, 92 percent of these early-stage patients who had surgery were still alive, says study coauthor Claudia I. Henschke, a physician at the Weill Medical College of Cornell University in New York City. Typically, only 50 to 70 percent of early-stage patients survive 5 years.
Although the study is a welcome foray into lung cancer screening, it doesn’t establish CT scanning as an effective test, says pulmonologist Michael Unger of the Fox Chase Cancer Center in Philadelphia.
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The study lacked a separate group whose outcomes the researchers could compare with those of people getting CT screening. Such a population could have gotten chest X rays or no screening at all.
Moreover, the biological nature of the cancers wasn’t elucidated, Unger says. That means that the scientists didn’t know whether they were catching aggressive cancers or just removing very slow-growing tumors that wouldn’t have spread and ultimately killed the patient, says Denise Aberle, a radiologist at the University of California, Los Angeles School of Medicine.
Attacking a suspected tumor with an array of invasive medical procedures can lead to “emotional, economic, and medical risks” for the patient, Aberle says. “Intuitively, we think that screening offers a better chance of survival. But we don’t know [in this case] whether the potential benefit will outweigh the potential harm.” The CT scans in this study resulted in lung biopsies of 43 people who turned out to have no malignancies.
For now, Unger says, asking a doctor for a CT scan as a test for lung cancer is like “opening a Pandora’s box.”
The screening debate probably won’t be settled until 2009. That’s when the first results will emerge from a large U.S. trial by Aberle and others comparing mortality from lung cancer in people screened with either CT scans or chest X rays. A similar trial is under way in Europe.
“This is only a salvo in the battle” to determine how best to screen for lung cancer, Unger says. “The war is not over.”