This could be an early sign of more honesty where it concerns new screening tests. In the not-so-distant past, screening tests were introduced to physicians and the general public with great enthusiasm but virtually no acknowledgement of harm. Too often that information came 20 to 40 years later (think PSA and mammography), if at all. Now low-dose lung scans have just received the official blessing as a screening test from four major professional organizations, including the American Cancer Society. Here’s what stands out—not only are the known harms acknowledged but so are the uncertainties.
The stamp of approval comes after an in-depth review of all relevant studies that appeared recently in the Journal of the American Medical Association. Here is the conclusion: “Low-dose computed tomography screening may benefit individuals at an increased risk for lung cancer, but uncertainty exists about the potential harms of screening and the generalizability of results.”
Let me translate this less-than-ringing endorsement. The rate of lung cancer deaths avoided by this expensive high-tech procedure is extremely low, despite the fact that it was confined to heavy smokers and former heavy smokers who quit in the last 15 years. More on deaths-avoided later.
As for the “generalizability of results” this refers to an underappreciated point that applies to most findings from clinical trials. The care delivered in a clinical trial is usually far better than that delivered in the real-world practice of medicine. Yet the single large clinical trial that formed the basis for the new review is an unusual mix of both. The diagnostic workups and treatments of the trial took place in the real world (academic medical centers, community hospitals, or doctor-owned radiology clinics). But all the images were interpreted by radiologists, who had extra training in the interpretation of low-dose CT scans and more experience with this particular technology than the average radiologist.
This government-funded study, called the National Lung Screening Trial, was described in the review as “the most informative.” It is the largest study (52,000 participants) and the only one that randomly assigned high-risk people to undergo either a CT scan or another already-discredited screening test (chest x-ray). All participants had one screening procedure annually for three years and then were followed for three more years.
Attempts were made to assess the harms. For example, the reviewers estimate that one cancer death would be caused by the radiation exposure of three scans “for every 2,500 persons screened, although this death would likely occur many years later.” Short-term estimates of false-alarms and unnecessary lung biopsies were mentioned. Amazingly, so was overdiagnosis (defined as “histologically confirmed lung cancers identified through screening that would not affect the patient’s lifetime if left untreated. This includes patients who are destined to die of another cause.”) Unfortunately, the reviewers say, “The rate of overdiagnosis [and the inevitable overtreatment] cannot yet be estimated.” Such gaps in information explain why “uncertainties about potential harms” appears in the review’s conclusion.
Lung scanning was introduced over 20 years ago as a diagnostic test, but there is no reliable information about how long or how frequently it has been used as a screening test. The latter use is a money-maker for hospitals, especially those advertising their high-tech equipment directly to the public. It is unlikely that the first wave of screening customers was giving their informed consent since there was no information to provide until 2010. This is the year when the National Lung Screening Trial posted its preliminary results on the National Cancer Institute’s website.
The final results of this trial are central to the newly published review, and here is how its authors describe lung scanning’s lifesaving advantage over chest x-rays: “The chance of dying from lung cancer was 0.33% less over a three-year period.”
Put another way: 99.6% of high-risk smokers and former smokers will risk the adverse effects of this test but gain no lifesaving benefit. Put yet-another way, one lung cancer death avoided out of every 320 people screened.
This review is described as “a collaborative initiative of the American Cancer Society, the American College of Chest Physicians, the American Society of Clinical Oncology, and the National Comprehensive Cancer Network. Disclosure: I served as consumer representative on one of the committees within this collaborative. It struck me as downright stupid that we were not permitted to look at the most obvious consideration: Is this expensive technology cost-effective? Unlike countries with high-quality medical care systems, the U.S. has a toxic politial climate that does not allow this question to be explored. The word rationing would be hurled at any conclusion that indicates the answer is no.
Maryann Napoli, Center for Medical Consumers©
Screening scans for smokers and former smokers 2011 post describes heavy smokers and the National Lung Screening Trial in greater detail.
Are you a smoker or former smoker? 2010 post describes an earlier lung scanning trial and why its results are unreliable.