Early detection of cancer is often a key factor in successful treatment. When it comes to lung cancer, however, all screening methods are not created equal. In fact, getting an annual chest X-ray is no more likely to turn up evidence of lung cancer than normal visits to the physician. And chest X-rays are less likely to find early stage lung cancer than a low-dose helical computed tomography (LDCT) screening.
So says a new study published online Wednesday by JAMA, The Journal of the American Medical Association. (The study will also appear in the November 2 issue.) The benefits of annual chest X-rays as a means of reducing the number of lung cancer deaths have been in question for some decades. In the JAMA study, researchers from a wide variety of institutions, including the National Cancer Institute (NCI) and the University of Minnesota's School of Public Health in Minneapolis, used data from a well-known cancer study to quantify the negligible impact of annual chest X-rays on a person's chances of dying from lung cancer, the leading cause of cancer deaths worldwide. There have been 221,130 new cases of lung cancer in the U.S. and 156,940 lung-cancer related deaths in 2011, according to the NCI.
The researchers studied data generated by the Prostate, Lung, Colorectal, and Ovarian (PLCO) Cancer Screening Trial. The PLCO, an NCI cancer study that lasted from 1993 to 2009, examined nearly 155,000 patients ages 55 through 74 years. Half of these patients underwent annual chest X-ray screening for up to four annual screens. The other half were not recommended for annual screenings but did receive normal medical care from their physicians as needed during that time. Both groups shared roughly the same demographics, including smokers vs. nonsmokers.
When the PLCO study was designed, prior studies on the benefits of chest X-rays had been inconclusive, says Christine Berg, chief of the NCI's Early Detection Research Group and a senior author on the JAMA paper.
Over the 16 years that the PLCO covers, 1,696 lung cancers were detected in the group that had been recommended for annual chest X-rays. Nearly the same number of cancers (1,620) was found in the group that had received normal care. Likewise, the researchers found that annual chest X-rays for up to four annual screens did not significantly decrease lung cancer mortality compared with usual care—1,213 lung cancer deaths were reported in the group receiving screenings, whereas the second group had 1,230 deaths.
There is no generally accepted screening test for lung cancer, according to the NCI. In addition to chest X-rays, researchers have tried testing sputum (mucus brought up from the lungs by coughing) for signs of cancer.
LDCT also has been proposed as a potential screening tool and fared much better than chest X-rays in the NCI's National Lung Screening Trial (NLST), launched in 2002. The NLST was a randomized national study involving 53,454 current and former heavy smokers ages 55 to 74—the same age range as the PLCO trial. "Currently low-dose helical CT screening has been shown in the National Lung Screening Trial to reduce lung cancer specific mortality by 20 percent," says Berg, also a co-investigator on the NLST trial. (Results from that study were published August 4 in the New England Journal of Medicine.)
"The PLCO lung cancer study result provides convincing evidence that lung cancer screening with chest radiography is not effective," Harold Sox, a professor of medicine at Dartmouth Medical School, wrote in a JAMA commentary accompanying the analysis of the PLCO trial. "The study is important for putting this question to rest and providing strong empirical grounds for comparing low-dose CT to a real-world alternative: usual care." Further, Sox wrote, "The NLST showed convincingly that early detection can lower the risk of death from lung cancer, a big step forward."
Whether the NLST encourages universal cancer screening has been the subject of debate, as reported in a 2007 Wall Street Journal article. Skeptics of universal screening say it leads to complications from biopsies (needed to confirm CT scan results) and unnecessary surgery.
For now, the best way to reduce one's chances of dying from lung cancer are to avoid smoking, or for smokers to quit smoking, Berg says. Still, "we would still have lung cancers developing in former smokers as they got older for the next few decades," she adds.
New research into potential biomarkers for the early detection of lung cancer is also underway, Berg says, and the NLST has shown that in a high-risk group LDCT can lower mortality associated with lung cancer.
Image courtesy of Lange123, via Wikimedia Commons