An article in the April issue of Radiology reports the results of a study of the use of helical CT scanning as an approach for the early detection of lung cancer among high risk smokers (Swensen SJ, Jett JR, Hartman TE, et al. CT screening for lung cancer: five-year prospective experience. Radiology 2005; 235:259-265). A group of 1,520 adults ages 50+ was followed for four years, receiving a baseline chest CT scan and four annual follow-up CT scans. The purpose of the study was to determine whether this approach would save lives by detecting lung cancers earlier than they would otherwise be detected, allowing for earlier and more effective treatment.
The study found that CT scan screening did not significantly reduce lung cancer deaths. Nor did it result in a shift to the detection of more very early cancers. But this screening did create problems for patients because of a very high false positive rate. False positive tests mean the finding of a lung nodule on the CT scan that turns out not to be cancerous. About three-fourths of the patients had a lung nodule detected, and of these, only 4% turned out to have cancer. Thus, well over 1,000 cancer-free patients were told they had a lung nodule suspicious for cancer and had to have further diagnostic procedures, sometimes involving surgical or other procedures (i.e., biopsy).
The Rest of the Story
While chest CT scan screening of current and ex-smokers at high risk for lung cancer turned out not to have any benefit to them, it did cause significant morbidity and mental distress. Being told that one has a nodule that could be cancerous tends to create substantial anxiety. For many of these patients, they had to live with this unnecessary anxiety for six months or even a year before they were able to be told that there was nothing to worry about. For others, they had to undergo further diagnostic tests, sometimes surgery.
Even among patients with new lung nodules greater than 4mm in size detected (nodules that were not present on the initial CT scan), the false positive rate was 92%. This means that the overwhelming majority of patients with newly diagnosed lung nodules (92%) did not have lung cancer.
Because of the anxiety produced by being told that one has a potentially cancerous lung nodule as well as the significant morbidity (and even mortality) associated with some of the interventions used to definitively diagnose these nodules, this study reveals that the CT screening approach resulted in more harm than good for these patients.
In order for a screening test to be effective for a relatively uncommon disease (and lung cancer is still uncommon, even in high risk smokers), the false positive rate must be extremely low. In other words, the test must not detect a large number of nodules that turn out to be benign. Otherwise, these patients will suffer a great deal of unnecessary anxiety and possibly morbidity and mortality. There would certainly have to be strong evidence of a significant mortality benefit in the population to recommend the use of such a screening test. In this case, helical CT scanning simply does not meet these criteria.
In more general terms, the results of this study underscore the pointlessness of devoting substantial resources to lung cancer screening. We should be focusing our resources in the area where we know we can have an effect: prevention of lung cancer through interventions to prevent smoking initiation and encourage smoking cessation.
A central tenet of medicine is "first, to do no harm." Screening for lung cancer, even in high risk individuals, appears to violate this basic principle.