After years of debate, a gold standard study that examined whether specialized CT scans could detect lung tumors has found that they lowered patients' risk of dying from lung cancer by 20 percent.
Even though the study was stopped early because of the benefits to patients who got the scans instead of conventional X-rays, there are enough "buts" about the results to make it clear that this sort of screening isn't ready for widespread use.
First off, the results apply only to older smokers and former smokers (those 55 to 74) who have burned up at least a pack of cigarettes a day for 30 years. That, the researchers say, represents heavy exposure to carcinogens.
Here's another caveat. While periodic computerized tomography scans (annually for three years) found suspicious nodules and other abnormalities in 1 of 4 of these high-risk patients, most of them weren't a problem.
The vast majority of these turn out to be false alarms after further testing, including more CT scans, lung biopsies (with a long needle) and surgery.
Still, after randomly assigning 53,000 such high-risk patients to low-dose CT screening or regular chest X-rays and watching what happened to them over as long as eight years, the federally funded National Lung Screening Trial found a modest reduction in lung cancer deaths — 442 among those who got chest X-rays versus 354 among those who get CT scans.
That's a 20.3 percent reduction in lung cancer deaths for the CT group — less than many had hoped for. Even so, it's a significant finding for the deadliest form of cancer. Lung cancer kills nearly 160,000 Americans each year – nearly a third of all cancer deaths.
The numbers suggests widespread CT screening could avoid tens of thousands of deaths. But you can't just apply the 20 percent reduction to all lung cancer deaths. Some of those involve people who never smoked and others are either young never smoked as much as the people in the new trial.
Screening "has the potential to save many lives among those at greatest risk," says Dr. Harold Varmus, director of the National Cancer Institute, which paid around a quarter-billion dollars for the National Lung Screening Trial.
Varmus was quick to add, in a teleconference to announce the results, that "no one should come away…believing that it is now safe to continue or start smoking" because CT can catch some lung cancers when they're early and curable.
So what happens next? A lot more analysis and, inevitably, a lot more argument about how to implement a screening program that takes into account factors like these:
- Who should get screened and how often?
- Who will pay for it (not just the screening CT but the inevitable followup tests)?
- How to weigh the costs and risks (including radiation exposure) against the benefit.
"Conceptually it's staggering to imagine that tomorrow we should be screening every individual who smokes or has smoked, and the data don't support that," says Dr. Peter Bach of Memorial Sloan-Kettering Cancer Center. Even so, he says, screening just the ones who resemble those in the new federal trial "would be a huge number of people."
That's why it's important to digest the results and to devise a sound public health strategy first, he says.
The process will begin in the next few months, as the National Cancer Institute and study authors pull together data for formal publication.
There wasn't time to do that before the announcement. The trial was halted on October 20 after a panel of experts determined that the study had answered the question is was intended to – does CT screening reduce lung cancer mortality in the studied patients? Yes.