Announcer: Tom Whitherspoon holds onto wonderful memories of a 45-year marriage. His wife died last year of lung cancer. They both were heavy smokers and now Tom is concerned about his own health.

Mr. Whitherspoon: "At the end, to watch her as I sat there holding her hand, gasping for breath as she died. I mean, it's not an experience I ever want to go through again."

Announcer: Tom Whitherspoon and many researchers hope that finding cancerous tumors before they cause symptoms will benefit people by lowering deaths from lung cancer. But when it comes to lung cancer, doctors aren't sure earlier detection makes treatment more successful.

Dr. Gohagan: "Spiral CT is a new technology which has been shown to detect small lesions in the lungs, smaller than you can find with a chest X-ray, but we don't know whether finding these lesions and treating them will actually lead to benefit for people. We don't know if a spiral CT is better than an X-ray."

Announcer: To find out if either test will reduce deaths from lung cancer, NCI is looking for 50,000 volunteers for a landmark 8-year study. The National Lung Screening Trial, or NLST, will be the biggest lung cancer screening study ever undertaken. Half of the participants will be screened by chest X-ray, the other half by Spiral CT. All will be randomly assigned.

Dr. Aberle: "At this time, there's no effective screening test for lung cancer, and yet it's the largest cause of cancer deaths in this country. I think many people don't understand the magnitude of the epidemic of lung cancer."

Announcer: The NCI trial will also look at the benefits and the risks of screening. Those risks exist because abnormalities seen on screening tests must be followed up by additional invasive tests that have risks of their own, just to determine whether or not the screening abnormalities are really cancer.

Dr. Gohagan: "Screening tests that turn out to be positive are followed up by diagnostic procedures and some of those procedures have risks associated with them."

Announcer: The stakes are high for the estimated 90 million current and former smokers in the United States who are at higher risk for lung cancer. Today, more Americans die of lung cancer than from prostate, breast, colon, and pancreatic cancers combined.

Dr. Aberle: "The hope is that this trial will lead to saving thousands of lives of people in this country."

Announcer: Male and female smokers and former smokers, age 55 to 74, may join NLST. Screening for participants is free of charge.

For more information about the clinical trial, call toll-free 1-800-4-CANCER.

This is Tom Hendrick reporting.