A study in the New England Journal of Medicine offers the strongest evidence yet that screening smokers periodically for lung cancer can save lives.

Lung cancer kills about 162,000 Americans a year and is the leading cause of cancer death in men and women. Only 15 percent of people with the disease survive five years from the time it is diagnosed.

What it will take to prove that CAT scans are either useful or a waste of time and money is a matter of great controversy.

Some people, including many treatment advocates, think there is enough evidence to urge all heavy smokers to have routine CAT scans. Others, including researchers and policymakers in the government, say it is a question that will not be settled for five or six years, when other studies are complete.

The new research, which appears in today's issue of the New England Journal of Medicine, seems destined to heat up that argument.

"I think it provides valuable information on many things. What it doesn't do is prove that you can reduce the number of people who will die from lung cancer," said Gary J. Kelloff, an oncologist at the National Cancer Institute.

Laurie Fenton, president of the Lung Cancer Alliance, an advocacy group headquartered in Washington, said: "We think this is a breakthrough for lung cancer. I think we have enough data to move forward and apply this to a high-risk population."

In 1994, the study, called the International Early Lung Cancer Action Program, began screening smokers and former smokers, as well as a few nonsmokers exposed to radon, beryllium and other cancer-causing substances.

In all, 31,567 people were screened. In the ensuing years, about 27,000 more scans were done, with some people having them annually. All were "spiral" or "helical" CAT scans in which the machine films the entire chest in the time that a person can hold a single breath.

About 13 percent of the baseline scans and 5 percent of the later ones found abnormalities. Many of these lump-shaped masses were watched with further scans to see whether they grew; others were examined with other imaging devices. Ultimately, 535 were biopsied to see if they were lung cancer -- and 484 were.

Of that group, 85 percent had small tumors that had not spread. Such early lung cancers can usually be cured; the problem is that they are usually found at that "asymptomatic stage" only by chance when someone has a CAT scan or chest X-ray for an unrelated reason.

Nearly everyone in the study with one of these "Stage I" tumors had them surgically removed, and 88 percent were alive five years later. Eight people who received no treatment -- the reasons were not specified -- died within five years.

"We have shown that when you diagnose it early that you can cure it," said Claudia I. Henschke of Weill Medical College of Cornell University, who headed the study. "We think this provides compelling evidence that you can save lives."

A study in the New England Journal of Medicine offers the strongest evidence yet that screening smokers periodically for lung cancer can save lives.
A study in the New England Journal of Medicine offers the strongest evidence yet that screening smokers periodically for lung cancer can save lives.

Some who disagree say the study had no controls -- no group randomly assigned to have no screening or to have some other kind of screening. Without a comparison group, it is impossible to say whether the outcomes of the smokers who received CAT scans was better.

It is not surprising that people whose lung cancers are found by a CAT scan survive longer than people whose tumors are found the usual way, after they cause pain or breathing problems. Screened patients receive diagnoses earlier and therefore will have the diagnosis for a longer time than someone whose tumor is found later, even if the two people die at the same time.

A study in the 1970s that screened smokers with chest X-rays every four months found exactly such contradictory results. The screened patients had a five-year survival rate of 35 percent, compared with 19 percent in the unscreened controls -- but the mortality rate from lung cancer was virtually identical in the two groups.

How could finding cancers when they are small ever be a bad idea?

Many experts say there is a chance that some small lung cancers will grow so slowly that they will never pose a health problem. This is true with some cases of prostate cancer and may be true of some cases of breast cancer, although the latter is less certain. Only a randomized controlled trial would be able to tell whether it is worth the risk, money, pain and emotional distress to find all small tumors and remove them.

Because many abnormal scans will lead to biopsies that involve sticking a needle into the lungs, "you need rather strong evidence that [screening] does what you think it does, namely reduces mortality," said Constantine Gatsonis, a biostatistician at Brown University.

The federal government is helping underwrite a $200 million study to try to do that. Gatsonis is one of the leaders of the National Lung Screening Trial, in which about 50,000 current or former smokers are being randomly assigned to receive three annual CAT scans or chest X-rays.

The third round of screening is almost finished, and results may be available in 2011 or 2012.