This week’s New England Journal of Medicine reported that annual chest computed tomography (CT) scans on those at risk for lung cancer can detect it earlier, at a more treatable stage. In the study, more than 31,000 people in the United States and overseas underwent spiral CT scans of their chests at the beginning and again in seven to 18 months unless something was detected on the first scan.
One and one-half percent of those screened had lung cancer and 85 percent of those with cancer had stage 1 — for which survival is best. After surgical removal of the cancer, 88 percent were expected to live at least 10 years; eight people who did not get treatment died within five years. The conclusion of the study’s authors was annual spiral CT screening can detect lung cancer that is curable.
From the news reports, one might think that smokers and others at risk for lung cancer should go out and get an annual CT scan. There is a lot of controversy about it, however. It was demonstrated years ago that routine chest X-ray does not find lung cancer early enough to save lives. CT scans are more sensitive, so this study looked at whether it would help to use CT for early lung cancer detection.
Lung cancer is notorious for showing symptoms only after it has advanced beyond the treatable stage. Early detection could be a boon to those at risk. So why are doctors not keeping the CT scanners busy day and night?
One concern is that there was no control group. Many cancers, even some lung cancers, may grow slowly and in some cases, the body’s immune system cures the cancer. The survival rate was estimated since some were followed less than 10 years. If compared to a similar group of people who did not get annual CT, it might have shown that early detection did not improve survival as much as estimated. Most people at risk for lung cancer also are at risk for heart and other lung diseases which could kill them before the lung cancer. Many who have cancer detected might be too ill to have lung surgery. It’s possible early detection might not really be that helpful.
Then there is the radiation dose. The participants in this study received two CT scans unless an abnormality was found that required more scanning. Every CT scan carries a dose of radiation, and its effects accumulate over time. Measuring the dose of radiation is tricky and subject to estimates and variability, so it’s difficult to say exactly how much radiation a person gets from a chest CT. Depending on how the dose is estimated, one CT scan of the chest is approximately equal to 100 chest X-rays at the skin surface and about half that to the center of the chest.
Also not clear is at what age screening would begin. A smoker or other person at risk for lung cancer who gets an annual CT scan for 10 years will have absorbed the radiation of 1,000 chest X-rays. Radiation itself is a potential cancer-causing agent. The radiation might not be such a problem for an 80-year-old former smoker who has less than a decade to live, but what about a 50-year-old?
The other issue is cost. Other studies have looked at CT scans for lung cancer detection. In some studies it was estimated that if everyone at risk were screened only once, it would cost more than $100,000 to save one life. Annual screening could cost more than $2 million per year of life saved. The general rule of thumb to decide cost effectiveness is a cost under $100,000 per year of life saved.
Unfortunately, we do not have sufficient evidence for a screening test for early diagnosis of lung cancer yet. The National Cancer Institute has several trials in progress that might shed some more light on the issues around lung cancer screening. In the meantime, quitting smoking will do the most to reduce the risk of lung cancer for the smoker and those subject to secondhand smoke.