According to the results of a large study, chest CT scans performed annually as a lung cancer screening test can reduce the risk of lung cancer death by 20% in current and former heavy smokers.
To reach these conclusions, federally funded scientists performed a multi-center trial in which they enrolled 53,000 people between the ages 55 and 74 that had at least a 30 pack-year history of smoking. Participants were randomized to receive either a chest x-ray or a CT scan at trial entry and then again one year, and 2 years thereafter. Ex-smokers that had quit within the last 15 years were enrolled as well.
The enrollees were followed for up to 5 years. There were 354 lung cancer deaths in the group that was randomized to receive CT scans, and 442 deaths in those receiving chest x-rays. The difference was large enough to prompt the study’s overseers to halt the study before its planned completion date, and to publicize the findings even before the write-up appeared in a peer reviewed journal.
Lung cancer kills nearly 160,000 people per year in the US. That’s more than the combined annual deaths from breast, colorectal, prostate and pancreatic cancers combined.
Previous studies had ruled-out chest x-rays as useful screening tests for the scourge, because they caught the disease too late. Not surprisingly therefore, many scientists hailed the news as a major advance in lung cancer screening.
“This is the first time that we have seen clear evidence of a significant reduction in lung cancer mortality with a screening test in a randomized controlled trial,” the National Cancer Institute’s Christine Berg told the New York Times.
Statements like this seem premature to me. Chest CT scans cost between $300-1,000 per test. There are nearly 90 million Americans who smoke or used to smoke. A widespread screening program using this technology would cost tens of billions of dollars per year in direct costs alone.
That’s not counting the indirect costs. In the present study, fully 25% of the subjects who were randomized to receive a CT scan were found to have a false positive result (an abnormality that turned out not to be cancer). Many of these false positive results undoubtedly triggered additional scans, lung biopsies and even thoracic surgery which drive up the overall costs of the screening program many times over.
It’s not clear that our overburdened health system can accomodate the cost escalations implied by a widespread CT scan-based screening program for lung cancer.
Beyond this, CT scans, even the newer “Spiral” scans, are associated with modest levels of radiation exposure in their own right. The cumulative effects of this can actually cause cancer.
And that 20% mortality reduction? That statistic can, in itself, be deceiving. According to Jaan Sidorov’s calculations over at Disease Management Care Blog, the absolute cancer death percentages in last Friday’s study were 1.3% for subjects receiving the CT scan and 1.7% in those receiving chest x-rays. The absolute difference in death rates was therefore about 4 in a thousand. More than 98% of both groups didn’t die of lung cancer during the study period, and the direct cost per life saved was $180,000. That’s an awful lot of CT scans, and an awful lot of money to achieve that reduction in absolute risk.
Perhaps where this is headed is a focused screening program for older adults with a history of heavy cigarette consumption. These folks have the greatest risk of lung cancer and are the least likely to sustain deleterious effects due to cumulative radiation exposure from the CT scans themselves.
Regardless, we all need to take a deep breath and wait for this study to be written-up and published in a peer reviewed journal. And we need to wait for the results of a cost-effectiveness analysis of this emerging technology before we get too wound-up over this promising, but early finding.