In the wake of the revelation that ABC News anchor Peter Jennings has been diagnosed with lung cancer, many of the nation's smokers and ex-smokers are experiencing anxiety about their own risk of developing lung cancer. Several newspaper articles have mentioned the availability of a new technique - low-dose spiral CT scanning - to detect lung cancer. Desite the potential promise of this screening method, I do not believe the evidence available now supports a recommendation that all concerned smokers and ex-smokers, on a population basis, be screened for lung cancer.
I am aware of no medical organization that has recommended the use of CT scans for detection of lung cancer in asymptomatic individuals, including smokers. The scientific and medical bodies that have examined this issue have concluded either that lung cancer screening of asymptomatic smokers is not recommended or that there is insufficient evidence of the potential harms and benefits to recommend screening at this time.
Here is what the major bodies have recommended:
- U.S. Preventive Services Task Force (2004): "The U.S. Preventive Services Task Force (USPSTF) concludes that the evidence is insufficient to recommend for or against screening asymptomatic persons for lung cancer with either low dose computerized tomography (LDCT), chest x-ray (CXR), sputum cytology, or a combination of these tests."
- American Cancer Society (2000): "At this time, the ACS does not recommend routine screening for lung cancer among the general adult population or in individuals who are at higher risk due to tobacco or occupational exposures."
- Canadian Task Force on Preventive Health Care (2003): "The CTF concludes that there is insufficient evidence (in quantity and/or quality) to make a recommendation as to whether spiral CT scanning should be used for screening asymptomatic people for lung cancer."
- American College of Chest Physicians (2003): "For individuals without symptoms or a history of cancer, the guideline developers recommend against the use of a single low-dose computed tomography scan (LDCT) or serial LDCTs to screen for the presence of lung cancer."
While there is some evidence (primarily from the Early Lung Cancer Action Program [ELCAP] study) that chest CT scanning can pick up substantially more tumors than chest X-ray and can shift the detection of cancers toward stage I, there is as yet no published evidence that this approach can reduce mortality. More troublesome, however, is the fact that the most recent published study (the Mayo Clinic study) failed to find any benefit of CT screening, either in terms of a shift toward detection of stage I cancers or in terms of decreased mortality.
While this could simply suggest that the methods used in the Mayo Clinic study were not as sophisticated as those used in ELCAP, it points out that the simple fact that a technology exists that can detect cancer early does not mean that this technology will work if put into general practice at this time.
But most concerning is the extremely high proportion of false positive tests in both the ELCAP and Mayo Clinic studies. Even in the ELCAP study, the positive predictive value of CT screening was only 12%. This means that 88% of patients with a lung nodule diagnosed on CT scan turned out not to have cancer. The anxiety created by the finding of a lung nodule is substantial, and at sites that do not have diagnostic follow-up procedures as carefully developed as with ELCAP or with radiologists who have as extensive experience in interpreting follow-up CT findings, many of these false positives will lead to morbidity and even mortality from invasive diagnostic tests.
Based on the published ELCAP findings (and this is a conservative estimate, as most CT scanning sites in the country do not have the kind of experience that ELCAP radiologists have), if the 92 million smokers and ex-smokers were to be screened, approximately 21 million individuals would be diagnosed with lung nodules, and 19 million of these people would have no malignant disease. Is it really fair to these 19 million people to get them all alarmed about their potential lung cancer risk and then for them to find out they do indeed have a lung nodule, but to make them either undergo invasive procedures or simply have to wait 6 months or a year with this anxiety, only to have them find out that nothing is wrong? Especially when we do not have sufficient published evidence to conclude that screening will save lives and that the benefits will outweigh the risks?
While I am open to the possibility that at some point in the future, the evidence will swing in favor of the routine use of chest CT for early detection of lung cancer in asymptomatic, high-risk patients (such as smokers), there simply is not sufficient evidence at this time to support a recommendation for population-based screening of smokers and ex-smokers.
Smokers should certainly quit smoking now to reduce their lung cancer risk, but there is no reason for a mass influx of the nation's 92 million smokers and ex-smokers into their doctors' offices to request a chest CT scan. There is not at the present time sufficient published evidence that warrants a conclusion that presenting to their doctors for lung cancer screening will have benefits to them that outweigh the risks that they will have to endure due to the enormously high false positive rate associated with this screening.
UPDATE (April 11, 2005; 11:50 pm): The American Council on Science and Health has released an excellent statement on this issue. The ACSH recommendations are evidence-based and acknowledge the increased anxiety about this disease among the public, especially ex-smokers. They do not try to channel this anxiety into a screening test that, as of yet has not been shown to have benefits that outweigh the costs of "needless anxiety and even needless surgery."