Maybe you're a smoker. Maybe you used to smoke a pack a day but quit twenty years ago (congratulations!). Maybe you're not a smoker but you've lived with one for many years. Maybe you've never touched a cigarette, but you're alarmed that Dana Reeve, a never-smoker with a healthy diet, was recently diagnosed with lung cancer. Should you get screened?
All medical interventions, including cancer screening, carry some risk, and the decision about whether to seek screening must be based on a comparison of these risks with the potential benefits. Unfortunately, it is difficult to do a benefit-risk analysis in this case because scientists are not yet sure if early detection does much to lengthen or improve the lives of lung cancer patients. In fact, randomized clinical trials (the most reliable types of studies) from twenty years ago report no reduction in lung cancer deaths from the use of screening. Interest has been renewed in widespread screening, however, because of recent improvements in high-resolution CT scanning technology.
Proponents of widespread CT screening point out that those whose asymptomatic cancers are detected through screening live longer from point of diagnosis than those whose cancers are not detected until they become sick. But in reality, there may not be a causal relationship there. Unlike colon or breast cancer, early detection of lung cancer does not necessarily lead to an improved outcome. It may appear that early detection prolongs life simply because patients start "running the clock" at an earlier point. In other words, if you walk from point A to point B, the trip takes just as long whether you start timing yourself at the beginning of the trip or in the middle. Lung cancer patients who wait until they are symptomatic to receive a diagnosis and start "timing themselves" probably are not taking a shorter trip (surviving for shorter lengths of time) than those who start timing earlier on -- it just appears that way. This is known as lead-time bias, and it makes studying the benefits of lung cancer screening very difficult.
Perhaps the greatest documented benefit of CT screening, though, is that patients who undergo it are more likely to quit smoking, presumably because of the "reality check" involved: 14% of the smokers in the Mayo Clinic cohort quit smoking after CT scanning as opposed to 5 to 7% in the general population. In another study, 23% of patients who underwent screening quit smoking in the next six months -- a higher success rate than drug-therapy interventions!
The risks of the procedure are slightly better defined. First, of course, there is the high cost of the procedure, which often is not covered by medical insurance. Second, there is the possibility of "false positives" -- abnormalities (such as scars and other benign lesions) that require investigation, even surgery, but turn out to be no real threat. Apart from the extreme anxiety that a false positive diagnosis creates, there is the potential for complications from invasive surgical procedures that may be done as a result; mortality and morbidity from some of these procedures are substantial. These risks may undermine the potential benefits of diagnosing lung cancer at an earlier stage.
The American Cancer Society recommends that CT scanning should not be performed on asymptomatic people. Until a study indicates that regular CT scanning improves survival rate and prognosis well beyond the risks of the screening, this is probably sound advice. Of course, if you do smoke, you are at much greater risk (approximately 90% of lung cancers are causally linked to cigarette smoke). If you are a former smoker, there is good and bad news: your risk of heart disease is reduced greatly soon after you quit, but unfortunately your lung cancer risk decreases much more slowly -- it may take over ten years to get your lung cancer risk back down to levels close to those of a never-smoker. If you are a smoker or former smoker, you may want to discuss the pros and cons of CT scanning with your doctor. If you don't fall into either of these categories, there is probably no reason to pursue testing for lung cancer at this time -- but don't forget that screening can be very beneficial for some other types of cancer.
Source: Mulshine, J. and Sullivan, D. Lung cancer screening. New England Journal of Medicine. Vol. 352: 2714-2719.
Mara Burney is a research associate at the American Council on Science and Health.
