Lung cancer screening is probably the most urgent topic in thoracic imaging. There is currently a very interesting debate about the use of low dose chest CT for this purpose. by Charles S. White, MD*


Lung cancer screening is probably the most urgent topic in thoracic imaging. There is currently a very interesting debate about the use of low dose chest CT for this purpose, dividing two groups with different views of the state of the situation.

The advocate group believes that thoracic CT can save lives, by detecting more lung cancers at earlier stages – these cancers are, therefore, less widely spread, with presumably better long term outcome.

The investigators from the ELCAP (Early Lung Cancer Action Project) study, led by Dr. Claudia Henschke from the Weill Cornell Medical College in New York, were the original group in the US to use CT for lung cancer screening. Their more recent findings, based on the 2,968 baseline and 4,538 repeat screenings, showed highly promising results as for the attainment of cure by early intervention. In many cases, patients have a survival benefit of ten to 15 years.

Chest CT is better than X-ray at detecting tumors when they are smaller than the average lung cancer. But does lung cancer always become fatal? That's still an open question. In the case of prostate cancer, many patients simply live with it and die of other causes. Whether the same occurs with lung cancer we still don't know.

The National Institutes of Health (NIH) and the National Cancer Institute (NCI) say the data available to date are insufficient to prove that screening is effective. Their main argument is that the CT screening may detect lots of slow growing, non-fatal tumors as well. They also say it's premature to say the method does work because there isn't a control group of people not having CT. They claim there needs to be a randomized study if you are going to look for improved mortality, which is considered a better standard than survival.

Another study that will add data to the debate, the National Lung Screening Trial (NLST), may address some of these needs. Launched in September 2002, it was designed to determine if screening with either spiral CT or chest X-ray before the appearance of symptoms can reduce deaths from lung cancer using a randomized approach. The control group, however, is getting chest X-rays and the critics argue that they should not be getting any lung cancer screening because none is currently recommended. Some have also criticized the study for not following patients for a long enough time to detect a difference between the CT screened group and the control group.

The arguments against the use of chest CT for screening are both scientific and financial. In the original Cornell study fewer than ten per cent of the nodules found were cancer. In a subsequent Mayo research, less than five per cent of them were malignant. Finding more benign nodules results in a larger number of biopsies, which increases the risk of lung collapse and other complications, extends hospital stay etc. – and insurers tend to be conservative.

In the US there are 170,000 deaths caused by lung cancer annually. If studies show that CT can save large numbers of lives, then it's worth the investment, which would amount to $20bn to start with, assuming a cost of $200 per CT scan. Until Medicare decides to reimburse it, however, the method won't go ahead. Nobody is likely to pay for it unless the evidence is very convincing.



* Dr. Charles S. White is Professor of Radiology and Medicine and Chief of Thoracic Radiology at the Department of Diagnostic Radiology, University of Maryland Medical Center.