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Posts Tagged ‘overdiagnosis and screening tests’

An honest take on screening for lung cancer

Posted by medconsumers on June 26, 2012

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©
Related posts:
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.

Posted in Cancer, hospitals, Lung surgery, Men's Health, radiation exposure, Scans and X-rays, Screening, surgery, testing, Women's Health | Tagged: , , , , , , , , , | 1 Comment »

What MDs don’t know about cancer screening

Posted by medconsumers on March 8, 2012

Most primary care physicians are keen on cancer screening. In fact, sending symptom-free patients for regular tests is central to their practice. Yet an understanding of cancer screening statistics is critical to informed decision-making, whether you’re the doctor sending people for tests or a patient just following orders. A new survey of U.S. primary care physicians shows the majority accept misleading statistics as proof that screening works.

Four hundred and twelve physicians took the online survey, which was designed by an American and German research team with a history of trying to improve understanding of health statistics by health professionals as well as the general public. “Most physicians incorrectly equated improved survival and early detection as evidence of lives saved,” concluded the researchers led by Odette Wegwarth, PhD, Max Planck Institute for Human Development, Berlin, Germany. “Few correctly recognized that only reduced mortality in a randomized trial constitutes evidence of the benefit of screening.” The survey results were published this week in Annals of Internal Medicine.

The survey presented physicians with two ways of expressing the effect of a hypothetical screening test which was described as improved 5-year survival and increased early detection in one scenario and as decreased cancer mortality and increased incidence in the other. Though the type of cancer was not identified, the hypothetical test scenarios were based on real-life data from the European prostate-cancer screening randomized trial. And the 5-year survival statistics and the percentage of stage I prostate cancers came from the U.S. database of cancer statistics collected in 1975. To be safe, that year was chosen because it predates the introduction of any organized screening program for prostate cancer.

The physicians were more impressed with what the survey authors called “irrelevant evidence,” for example, a test with a large 5-year survival rate. Here’s why this is irrelevant: The older we get, the more cancers we have in our bodies; many will never become life-threatening. Prostate cancer, for example, is in the overwhelming majority of cases a slow-growing or non-progressive cancer.

Therefore, prostate cancer’s 5-year survival rate will look like a clear justification for early cancer detection because most men will die of something else. Conversely, they  could die six years after a diagnosis of prostate cancer and still be counted as a “survivor”. Furthermore, screening often moves up the time of diagnosis (and treatment) without moving back the time of death.  (By the way, we can thank the American Cancer Society for its long-time use of this extremely misleading measurement of a cancer screening test’s benefit. In the not-so-distant past, the ACS actually used the word ‘cure’ interchangeably with 5-year survival, thus making generations of cancer patients think that making it to five years meant something.)

Now for the other worrisome finding:  The surveyed physicians were less impressed with a test described as having “reduced mortality”. And they were more impressed with a test that finds lots of cancer. But screening for cancer will always increase the number of cancer cases diagnosed, compared with the number of cancers found in people who seek medical attention only after symptoms appear. That’s because screening detects many more cancers that do not progress, which falsely inflates the apparent benefit of a screening tests (a phenomenon that the survey authors describe as overdiagnosis). This is why careful researchers will—after many years of follow-up—-compare the overall death rate of both the screened and unscreened groups. It is the only way to sort out the people who actually achieved a life-saving benefit from those who were treated unnecessarily for a cancer they didn’t need to know about.

This comparison is also a way  for researchers to determine screening’s “cost” in terms of harms. Here’s what the European prostate cancer screening trial found:  For every one prostate cancer death avoided in the PSA screened men, 48 men suffered severe complications from unnecessary treatment of a non-progressive cancer.

What to do

If you are going for any cancer screening test, inform yourself first at the National Cancer Institute’s website.  And be sure to use the “health professional” version which is more honest and in-depth than the patient version. If you get most of your medical information from the media, plan on regular visits to this media fact-checking website (www.Healthnewsreview.org). See its recent excellent critique of the media’s take on the latest colon cancer screening research, particularly The New York Times’ erroneous portrayal of it as definitive proof for colonoscopy as the best screening method. Click here

Maryann Napoli, Center for Medical Consumers©

Related posts:
Most drug don’t work (This is about understanding drug trial statistics.)
PSA screening for prostate cancer
Cancers that do not kill
Reduce your risk of breast cancer: Avoid mammograms (unless you have a breast symptom)

Posted in Cancer, colon cancer, Doctors, Screening, testing | Tagged: , , , , , , , , , | 1 Comment »

 
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