The National Cancer Institute isn't changing one of its key messages: don't smoke--it'll kill you.
But the mortality data from its ongoing National Lung Screening Trial (NLST) involving more than 53,000 current and former heavy smokers ages 55 to 74 is so striking that the institute announced initial findings today, ahead of a more comprehensive report.
What the trial shows is that there have been 20 percent fewer deaths from lung cancer among trial participants who receive an annual low-dose CT scan than those who receive an annual standard chest X-ray.
While CT scans are already considered valuable in screening for lung and other cancers, this is the first trial to show that the screening method results in a statistically significant lower mortality rate compared to X-rays. The Institute published a paper on these findings yesterday in the journal Radiology.
"The results of this trial provide objective evidence of the benefits of low-dose helical CT screening in an older, high-risk population and suggest that if low-dose helical CT screening is implemented responsibly, and individuals with abnormalities are judiciously followed, we have the potential to save thousands of lives," says NLST principal investigator Denise Aberle.
With the health risks of radiation exposure from CT scans hotly debated, physicians will likely be weighing the risks of getting scans alongside the risks of not getting them.
An estimated 80 million people in the U.S. are current or former smokers. More people die from lung cancer in the U.S. every year (160,000) than from pancreatic, breast, prostate, and colorectal cancers combined, and 85 percent of those diagnosed with lung cancer die from it. So a 20 percent reduction among heavy smokers could add up to tens of thousands of lives saved every year.
Helical CT uses X-rays to obtain a multiple-image scan of the entire chest during a 7- to 15-second breath-hold, while a standard chest X-ray results in a single image, with anatomic structures overlapping one another, although this method requires only a sub-second breath-hold.
The 53,500 men and women who signed up for the trial at 33 locations in 2002 had to have at least a 30-pack-year smoking history (determined by multiplying the number of packs smoked a day by the number of years smoking). They were assigned randomly to receive CT scans or X-rays. They received one scan at the outset and two more in the following 20 months. Since then, 354 in the annual CT scan group died from lung cancer, 20 percent fewer than the 442 deaths in the annual X-ray group.
But the findings revealed something else. The total (796) deaths from lung cancer comprised only 25 percent of the total number of deaths in the group as a whole; the other 75 percent died from other causes, such as cardiovascular disease. Out of the total deaths from any cause--roughly 3,200--the group with annual CT scans still had a 7 percent lower mortality rate.
One longtime advocate of CT scans in lung cancer screening tells The New York Times that this is because the scans also help screen for cardiovascular and other diseases, and that had participants been scanned over a longer period, even more lives would have been saved: "What we also have found is that low-dose CT scan gives information on cardiovascular disease, emphysema, and other pulmonary diseases," Claudia Henschke of Cornell University says. "Those are the three big killers of older people. There is just tremendous potential."
But CT scans remain both controversial and expensive. In the meantime, Aberle says she cannot overemphasize the bottom line: "The single best way to prevent lung cancer deaths is to never start smoking, and if already smoking, to quit permanently."