An eight year study, the National Lung Screening Trial, was recently stopped ahead of schedule when it became apparent to researchers that annual CT scans for past and current smokers at high risk for lung cancer decreased lung cancer mortality by about 20%. Study participants were those who had a “30-pack year” smoking history. (For example, a person who smokes one pack of cigarettes a day for 30 years has such a history, the same as somebody who smokes 2 packs a day for 15 years.)
This finding could potentially save hundreds of thousands of lives around the world each year as lung cancer is the most common cause of death due to cancer in the United States-for both men and women. Most lung cancer cases are due to smoking, and as the number of smokers in the world increases, so to will the absolute number of lung cancer deaths. Each year in the United States approximately 155,000 people die from lung cancer.
Because smokers are at such a high risk of developing lung cancer, doctors have often wondered if aggressive screening programs, such as those using CT scans, would save lives. A drawback to this approach is the fact that CT scans expose the patient to radiation. Just how dangerous CT scans are is unknown-although some newer research has expressed grave concerns about the radiation exposure.
In July of this year, a perspective in the New England Journal of Medicine noted that in 2007 over 70 million CT scans were performed, and that this radiation exposure may have caused 29,000 cancers. However, one expert, Dr. Rebecca Smith-Bindman, believes that the number may be even higher, perhaps as many as 900,000 cases of cancer caused by CT scan in the United States each year.
It is important to note that the use of CT scans to detect lung cancer in smokers involves exposing their lungs to radiation, which have already been damaged by smoking and could possibly be more sensitive to the ill effects of CT scan radiation. It will be important to follow-up the patients who participated in this study to determine whether they later have an increased risk of lung cancer, or another type of cancer, if they received annual CT scans.
However, this new study did use a newer type of CT scan called, “low dose” helical CT. This type of scan delivers 20 to 25% of the radiation of a standard CT scan. Though how many cases of cancer even lose-dose helical CT causes is at this point very unclear.
Interestingly, while the 20% drop in deaths from lung cancer in the group that got the low-dose CT scans was welcome news, researchers are unsure exactly why this happened. There is even a small possibility that the exposure to a small amount of radiation actually helped prevent lung cancer, perhaps by stimulating immune cells which then helped to keep new cancers in check.
Of course, radiation exposure is only part of the drawback to annual CT scans for those at risk for lung cancer, another is cost. Further studies will look at the cost of performing and reading the CT scan when compared with how many lives are expected to be saved from this screening procedure. In addition, a certain number of patients may undergo biopsies for suspicious lesions which turn out to be benign.
While more studies will be needed to clarify the role of low-dose CT scans for patients at risk of lunger cancer, what would most likely lead to a widely used screening test for lung cancer patients would be the development of a blood test which detects common types of lung cancer, or the development of a new type of screening technology which is as effective as CT scans, but which doesn’t use ionizing radiation.