CT scans and the national lung screening trial

Globally, lung cancer is the leading cause of cancer-related death, and recently surpassed heart disease as the leading cause of smoking-related mortality. The National Cancer Institute estimates that this year in the U.S., more than 222,000 men and women will be diagnosed with the disease and 157,300 will die. The high mortality rate is in part a consequence of the difficulty in diagnosing the disease. Using chest X-rays, physicians typically discover lung cancers only at an advanced stage.

To explore the potential of low-dose helical computed tomography (CT) scans to detect the disease earlier, a large-scale randomized controlled trial was conducted. The study report, “The National Lung Screening Trial,” was published in 2010. The study began in 2002 and involved more than 53,000 current and former heavy smokers ages 55 to 74. Each participant was given a baseline screening and two yearly examinations using either CT or a chest X-ray at 33 screening centers nationwide.

The study’s findings include:

• Compared with participants who were screened with chest X-rays, 20% fewer lung cancer deaths were reported among participants who underwent CT scans.
• Overall mortality rate among those who were screened with CT scans was 7% lower compared to those who underwent chest X-rays screening.

The National Cancer Institute stopped the study and announced the initial findings after the data provided a “statistically convincing answer” to the study’s primary question.

While the conclusions to be drawn from the study seem self-evident, an article in The New York Times, “The Downside of a Cancer Study Extolling CT Scans,” indicated that caution was nonetheless necessary. “One of every four lung scans showed an abnormality, which often led to additional worry, radiation exposure from follow-up scans and, sometimes, lung biopsies and even risky surgery,” the author wrote.

Moreover, the study focused on the benefits of CT scans for current and former heavy smokers; in lower-risk groups, “It’s likely that thousands of people would need to be exposed to the risks of screening before a single life was saved. And it’s possible that many of those scanned unnecessarily could be seriously harmed.”

Based on the study’s findings, the next steps would include drawing up clinical guidelines and policy recommendations for lung-cancer screening to balance the benefits of CT scans against the risks for at-risk as well as lower-risk populations.

Tags: cancer, safety, technology, tobacco