DiaLog: Helical CT Screening: Does It Affect Lung Cancer Outcome?

From OncoLog, November 2006, Vol. 51, No. 11

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Helical CT Screening: Does It Affect Lung Cancer Outcome?

Reginald F. Munden, M.D., Professor, Department of Diagnostic Radiology

Despite tremendous efforts over the past several decades, the overall 5-year survival rate for lung cancer is below 14%. This is partly because a significant number of lung cancers are not detected at an early stage. Recent advances in imaging include helical computed tomography (CT), which allows the whole chest to be scanned rapidly in a single breath-hold, thus greatly improving the ability to detect small cancers. For this reason, there is much interest in applying helical CT to lung cancer screening.

However, low-dose CT screening for lung cancer has proven to be a complex and controversial topic. The fundamental goal of screening is to detect disease at a stage when it can be cured. The screening test must carry low risk; be accurate, with an acceptable level of “false alarms”; be easily obtained; and be cost effective. There have been a number of studies of CT screening for lung cancer, but there is still much controversy as to whether helical CT screening meets these criteria.

In a recent study in the New England Journal of Medicine, Dr. Claudia Henschke and colleagues estimated a 10-year survival rate of 88% in patients who had stage I lung cancer detected by helical CT. To date, the results of all of these screening studies are very exciting, but so far they have shown only that helical CT can detect small lung cancers—not necessarily that this will affect the patient’s outcome.

The controversy is predominantly in two areas: the reduction in lung cancer mortality and the number of false-positive CTs (or false alarms). Studies indicate a longer survival time with CT screening, but this may be due to a longer lead time bias in which patients are diagnosed earlier—but die at the same time they would have if diagnosed later. In screening trials, it is mortality that truly reflects a screening test’s effectiveness, because the data are not subject to lead time biases.

The second major issue with helical CT is that many false-positive results will occur because of the test’s sensitivity. Several of the studies have reported that up to 70% of the people screened had abnormalities that needed further medical evaluation, few of which were subsequently found to be of clinical significance. In order for this level of potential false-positive findings to be acceptable, there has to be a significant benefit (i.e., reduced mortality) to the screening test.

More definitive data may be available in just a few years. The National Cancer Institute is sponsoring a large randomized controlled study to evaluate helical CT in lung cancer screening compared with chest x-ray. This study should be completed in 2009 and answer the question of whether screening with helical CT is effective in reducing lung cancer mortality.

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Other articles in OncoLog, November 2006 issue:

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