A provocative analysis suggests that lung cancer, the world's top cancer killer, isn't as deadly as doctors once thought, finding that almost 1 in 5 lung tumors detected on CT scans are probably so slow-growing that they would never cause problems.
These were not false-positives suspicious results that turn out upon further testing not to be cancer. These were indeed cancerous tumors, but ones that caused no symptoms and were unlikely ever to become deadly, the researchers said.
Still, the results are not likely to change how doctors treat lung cancer.
For one thing, the disease is usually diagnosed after symptoms develop, when tumors show up on an ordinary chest X-ray and are potentially life-threatening.
Also, doctors don't know yet how to determine which symptomless tumors found on CT scans might become dangerous, so they automatically treat the cancer 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.
A leader of an influential government-appointed health panel agreed.
"Putting the word 'harmless' next to cancer is such a foreign concept to people," said Dr Michael LeFevre, co-chairman of the US 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.
He called the study "a very important contribution," but said doctors will face a challenge in trying to explain the results to patients.
The study was published yesterday in the journal JAMA Internal Medicine.
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 Americans 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 may never advance to the point where they could be spotted on an ordinary chest X-ray.
An earlier report on the study found that 320 patients would need to get CT screening 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.
