Study shows some lung cancer tumors harmless
CT scans more sensitive than conventional chest X-rays
CHICAGO — A new analysis suggests that almost one in five lung tumors detected on CT scans grow so slowly that they never would cause harm.
They are not false-positives, suspicious results that turn out upon further testing not to be cancer. They are indeed cancerous tumors but ones that caused no symptoms and were unlikely ever to become deadly, the researchers said.
Still, the results probably will not change how doctors treat the world’s top cancer killer.
For one thing, the disease usually is diagnosed after symptoms develop. Tumors show up on an ordinary chest X-ray and are potentially life-threatening.
Also, doctors don’t know how to determine which symptomless tumors on CT scans might become dangerous, so they treat all the tumors aggressively.
The findings underscore the need to identify biological markers that would help doctors determine which tumors are harmless and which ones require treatment, said Dr. Edward Patz, Jr., lead author and a radiologist at Duke University Medical Center. He is among researchers working to do just that.
Patz said patients who seek lung cancer screening should be told about the study results.
“People have to understand that we’re going to find some cancers, which if we’d never looked, we never would have had to treat,” he said.
A leader of an influential government-appointed health panel agreed.
“Putting the word ‘harmless’ next to cancer is such a foreign concept,” said Dr. Michael LeFevre, co-chairman of the U.S. Preventive Services Task Force.
The panel recently issued a draft proposal recommending annual CT scans for high-risk current and former heavy smokers, echoing advice from the American Cancer Society. A final recommendation is pending, but LeFevre said the panel had already assumed that screening might lead to overdiagnosis.
“The more we bring public awareness of this, then the more informed decisions might be when people decide to screen or not,” LeFevre said. The study is “a very important contribution,” he said, but doctors will face a challenge in trying to explain the results to patients.
In testimonials, patients often say lung cancer screening via CT scans cured them. In many cases, however, the study suggests “we cured them of a disease we didn’t need to find in the first place,” LeFevre said.
The study was published Monday in the journal JAMA Internal Medicine.
More than 200,000 Americans are diagnosed with lung cancer each year, and more than half of them die. Worldwide, there are about 1.5 million lung cancer deaths annually. The new study is an analysis of data from the National Lung Cancer Screening Trial, National Cancer Institute research involving 53,452 people at high risk for lung cancer who were followed for about six years.
Half of them got three annual low-dose CT scans, a type of X-ray that is much more sensitive than the ordinary variety, and half got three annual conventional chest X-rays. During six years of follow-up, 1,089 lung cancers were diagnosed in CT scan patients, versus 969 in those who got chest X-rays.
That would suggest CT scans are finding many early cases of lung cancer that might never advance to the point where they could be spotted on a chest X-ray.
An earlier report on the study found that 320 patients would need to get CT screenings to prevent one lung cancer death. The new analysis suggests that for every 10 lives saved by CT lung cancer screening, almost 14 people will have been diagnosed with a lung cancer that would never have caused any harm, said Dr. Len Lichtenfeld, the cancer society’s deputy chief medical officer.
That is a higher rate of overdiagnosis than Lichtenfeld would have predicted, but the study shows how much understanding of cancer has evolved.
Decades ago, “every cancer was a bad cancer,” he said.
The American College of Radiology said the earlier study showed lung cancer screening significantly reduces lung cancer deaths in high-risk patients, which “significantly outweighs the comparatively modest rate of overdiagnosis.”