CT scans to detect lung cancer early can save lives, according to a study of 53,456 current and former smokers ages 55 to 74.
The study findings were announced by the National Institutes of Health (NIH) -- which funded the massive study -- on November 4.
The study, called the National Lung Screening Trial (NLST), marks the first time a screening test for lung cancer has been shown to improve the odds of survival. The study demonstrated that a low-dose, helical computed tomography (CT) exam -- lasting from seven to 15 seconds -- is significantly better than an X-ray for detecting life-threatening lung cancers at an earlier stage when treatment often is more successful.
During the course of the study there were 442 deaths in the group that received X-rays, compared to 354 deaths among those who received CT exams. So far, participants’ health has been tracked for up to seven years.
Rebecca Smith-Bindman, MD
“The results were pretty striking,” says Rebecca Smith-Bindman, MD, a UCSF radiologist and epidemiologist. “They showed a decrease in lung cancer mortality of 20 percent and a decrease in overall mortality of 7 percent. I think that’s really exciting.”
Just as they are used to detect breast cancer through X-ray mammograms, X-rays also can be used to detect many lung tumors. However, earlier studies on the costs and benefits of X-ray screening for smokers led to the rejection of X-rays for use in routine diagnostic screening for this group.
According to the trial design, the study was ended by an independent monitoring panel, because the life-saving benefit of CT screening already had become significant despite the fact that the trial was not yet completed.
“This is an enormous step forward for improving outcomes for lung cancer patients and for preventing thousands of deaths that would occur without screening,” says UCSF thoracic surgeon and lung cancer specialist David Jablons, MD. “CT screening of the appropriate population of patients saves lives in real time today."
David Jablons, MD
CT Screening for Lung Cancer Could Affect many Millions
The impact of a screening program could be great, as one in five adults in the United States is a smoker, a fraction that has not been nudged lower since 2005, according to the US Centers for Disease Control and Prevention.
The announcement of the results of the trial did not include any risk-benefit analysis, and no data on risks or negative outcomes due to screening. It is not yet clear what screening recommendations will emerge as a result of the study.
Widespread CT screening for lung cancer would lead to many false positive results -- abnormalities observed in CT images that with follow-up turn out not to be lung cancer. The rate of false positives has not yet been reported by the NIH.
False positive results can lead to many unnecessary lung biopsies. A lung biopsy is a major surgical procedure that poses its own risks, especially to older patients who may already have other smoking-related diseases such as emphysema.
Kathryn Phillips, PhD
Radiation Exposure and Risk-Benefit Analysis in the Real World
Smith-Bindman recently conducted an influential study on the cancer risks associated with routine CT exams. Many patients are unnecessarily exposed to radiation from unneeded exams or because of technician errors in programming or operating equipment, Smith-Bindman found.
In the NLST, Smith-Bindman says, “They were extremely specific and careful about the protocols they used. I think it will be equally important that there be similar standardization when this test is used outside the setting of a clinical trial -- both for the conduct of the exam, and for how you follow patients who have repeat examinations.”
When nodules are detected, the follow up should be a low-dose CT exam, yet many times physicians instead follow-up with high-dose exams, Smith Bindman says.
The risks posed by repeated exposure to radiation from low-dose CT exams are not clear, according to Smith-Bindman. Cancers that arise due to radiation are thought to normally take decades to become detectable. However, a study
published online October 25 in the Journal of the National Cancer
Institute suggests the middle-aged people may be at greater risk for cancer due to radiation than has previously been thought.
According to Kathryn Phillips, PhD, who leads the Center for Translational and Policy Research on Personalized Medicine at UCSF, “The finding that screening saves lives is only the first step in a larger analysis that needs to be done to assess the balance of benefits and costs. For example, what is the best way to determine who is screened? Is there a way to identify higher risk individuals for more intensive CT screening using less invasive and expensive tests, such as blood tests?”
“The bottom line is Americans tend to think more screening is better, although they often aren't fully aware of the downsides of screening. I hope there will be careful consideration of the pros and cons, from a broad perspective.”
Prevention is better than earlier diagnosis, and most lung cancers are preventable. “While this study demonstrates a substantial and important reduction in lung cancer deaths, if our patients would stop smoking or not start smoking, then lung cancer deaths would be reduced by 90 percent,” Smith-Bindman says.