A 55-year-old artist came to see me for evaluation of blood-count abnormalities that turned out to be merely the aftermath of a viral infection, so our conversation quickly turned to a more worrisome topic: the fact that she had smoked a pack of cigarettes a day for 30 years. She had quit five years earlier, and now she wanted to know whether she should be screened for lung cancer.

I walked her through the current incomplete state of our knowledge on this subject.

Lung cancer kills more Americans every year than breast, colon, cervix, and prostate cancers combined. The risk of developing the disease increases the longer and more heavily people smoke, especially if they’re still at it past age 50. Quitting helps a lot, but it takes five years after quitting for the risk to start dropping, and it doesn’t fall back to the level of never-smokers for at least 20 years, if ever. My patient was thus still at fairly high risk.

Survival statistics remain stubbornly dismal. Only about 16 percent of patients are still alive more than five years after their initial diagnosis because most don’t discover they have cancer until it has already spread to nearby lymph nodes or other organs. That’s too bad, because half of patients whose lung cancers are diagnosed before they spread survive at least five years, and those with the very smallest tumors may have even better survival rates.

But studies of screening with regular chest X-rays have found that they miss too many small tumors to reduce the overall lung-cancer death rate appreciably.

Now there’s another lung-cancer screening option: a technology called spiral CT scanning, which produces a much sharper, more-detailed image of the lungs than a regular X-ray, with about the same radiation exposure as a mammogram.

More than a half-dozen studies around the world have shown that this test is better than a regular X-ray for spotting lung cancers when they’re small and localized enough to be removed surgically. In a February 2006 report in the Archives of Internal Medicine, researchers from a major long-term study of spiral CT screening, the International Early Lung Cancer Action Program (I-ELCAP), reported that thus far, 85 percent of cancers found by the screening had not metastasized to nearby lymph nodes or other tissues. As encouraging as this is, the I-ELCAP study isn’t a randomized controlled trial that could prove for certain that spiral CT screening saves lives in the long run. Just such a study, involving 50,000 people and conducted by the National Cancer Institute, is under way now and may eventually answer that question, but results are years away.

Moreover, the screening has a downside: finding too many abnormalities. Scars from noncancerous smoking damage or old infections can be difficult to distinguish from malignancies. In the I-ELCAP study, only about one-eighth of suspicious nodules turned out to be cancer. But all suspicious findings require follow-up with additional scans, often just months apart, or a lung biopsy, a procedure that itself carries some risk of lung collapse or infection—not to mention the attendant anxiety. Moreover, once you’ve made the decision to screen, the test must be repeated every year to be of any benefit.

Based on research to date, we’re still not able to specify the type of smoking history that calls for screening. For now, the best advice is that if you ever smoked regularly, ask your doctor whether screening might be appropriate for you. If you decide to go ahead, try to get the screen as part of a clinical trial. That way, the doctor performing the screening will be experienced in interpreting and following up on the results.

The I-ELCAP study is still enrolling patients; a list of centers can be found at www.ielcap.org. Some of the centers offer free screenings while others charge up to $350 (most insurers won’t cover the initial testing, considering it’s still experimental, though they’ll likely cover any follow-up testing).

And of course, if you are still smoking, quit. Smoking is a direct cause of roughly 87 percent of lung cancers.

After some discussion and thought, my patient elected to have a spiral CT scan as part of the I-ELCAP study. It showed early signs of emphysema but no suspicious nodules. While the jury is still out on making lung-cancer screening a routine test for smokers and ex-smokers, my patient is happy to have had the test and will continue with yearly screening.