Will screening for lung cancer save lives?

Friday, September 05, 2003

Smokers and former smokers are often told they are at risk for lung cancer. But there's no accepted screening test for this cancer, which kills 17 Americans every hour.

The National Cancer Institute launched the National Lung Screening Trial (NLST) to determine if screening people with either spiral computerized tomography (CT) or chest X-ray before they have symptoms can reduce deaths from lung cancer. Nationwide, about 50,000 current and former smokers are needed.

Researchers at Mayo Clinic in Jacksonville are looking for 1,000 participants who will be randomly assigned to receive either a spiral CT or a chest X-ray once a year for three years. The tests are free. Researchers will contact the participants periodically until 2009 to check on their health. Current and former heavy smokers (generally people who smoke a pack a day or more) are eligible to join the NLST if they are between the ages of 55 and 74, have never had lung cancer, have not had any cancer within the last five years (except some skin cancers and in situ, or early stage, cancers), and are not currently enrolled in another cancer screening or prevention study.

"Lung cancer kills more people than any other kind of cancer including breast and prostate," says Dr. Elizabeth Johnson, a lung cancer specialist involved in the study at Mayo Clinic in Jacksonville. "Not smoking is the best way to keep lung cancer from ever developing. But quitting is very difficult for many people, and the effects of the cigarettes can last for years afterwards. A good screening test might provide us with the means of minimizing the chances someone dies from lung cancer."

More information is available from the NLST program at Mayo Clinic, (904) 953-2200.

Cancer facts

Americans lose more loved ones to lung cancer than to cancers of the breast, prostate, colon, and pancreas combined. The nation spends more than $5 billion each year taking care of people with lung cancer.

Background about lung cancer and screening tests

When lung cancer is found, the disease has already spread outside the lung in 15 to 40 percent of cases. Early detection may reduce symptoms, result in milder treatment with fewer side effects or prolong life, but scientists don't know these things will happen for sure. That's why the NLST is important.

Several large studies have found that routine chest X-rays are not a good screening tool to detect early lung cancer. But some experts say it's better than nothing and do use it to routinely check the lungs of smokers. However, X-rays can't see the entire lung and might miss very small cancers. A CT scan might overcome both of those difficulties.

Chest X-rays detect tumors as small as 1 to 2 centimeters (0.4 to 0.8 inches) in size. Spiral CT uses an X-ray machine that rotates around the person being screened and scans the entire chest in 15 to 25 seconds. A computer then assembles the images into a three-dimensional model of the lungs. Spiral CT can pick up tumors averaging about 1 centimeter. This size differential has helped spur some facilities with spiral CT to tout the scans as a new way to find early lung cancer in smokers and former smokers. Conventional wisdom suggests that the smaller the tumor, the more likely the chance of survival.

But a small tumor may not necessarily mean early lung cancer. Other factors determine whether a cancer metastasizes, or spreads, that have nothing to do with its size at diagnosis. So, finding small lesions may not change the death rate from lung cancer.

No scientific evidence to date has shown that screening for lung cancer by any method actually saves lives. NLST, because of the number of individuals participating and because it is a randomized, controlled trial — the gold standard of research studies — should determine whether spiral CT scans are better than chest X-rays at reducing a person's chances of dying from lung cancer.

Spiral CT is a very sensitive test. It detects smaller abnormalities than chest X-rays, but also more lung abnormalities than chest X-rays. Some of these abnormalities are cancers, but many — 70 percent or more — are benign scars or other lesions that will never cause disease. Finding these abnormalities, determining which ones are dangerous, and treating them may reduce lung cancer deaths. But maybe not.

It could turn out that screening with spiral CT will result in subjecting many healthy people to intrusive diagnostic and therapeutic procedures that carry the risk of medical complications and emotional distress. Finally, screening with either tool may not find cancers early enough to lower lung cancer deaths. The answers to these questions are the goals of NLST.

###

To obtain the latest news releases from Mayo Clinic, go to www.mayoclinic.org/news. MayoClinic.com is available as a resource for your health stories.