What MDs don’t know about cancer screening

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)

Overtreatment of early prostate cancer

In the 20 years since the screening PSA blood test for prostate cancer was introduced, it has become increasingly obvious that widespread use is causing far more harm than good—namely, the unnecessary treatment of cancers destined to remain dormant and never produce symptoms. The latest evidence comes from researchers who looked at treatment patterns of U.S. men whose cancers were detected at the earliest stage. The results raise questions not only about their overly aggressive treatment but also the PSA test level for sending them off for the biopsy which starts the whole process.

Keep in mind that doctors still cannot tell the difference between the prostate cancers that are going nowhere and the small minority that will turn aggressive and deadly. The new study found that over 75% of the men whose prostate cancers were least likely to spread or become lethal underwent a radical prostatectomy or radiation therapy. The severe adverse effects of each include impotence and incontinence.

The study, led by Yu-Hsuan Shao, PhD, Cancer Institute of New Jersey, appeared in the Archives of Internal Medicine. It drew on data from U.S. cancer registries, specifically about the treatment of 123,934 men with newly diagnosed prostate cancer from 2004 to 2006.

The advanced age of the men in this study is a cause for major concern. Almost 69% of men age 65 to 74 and about 40% of those over 75 had their prostates surgically removed or irradiated. This was described as “troubling” in the accompanying editorial because men 65 and older cannot expect any prostate treatment to prolong life. The editorialists, Richard M. Hoffman, MD, and Steven B. Zeliadt, PhD, cite a landmark 2005 Scandinavian trial that randomly assigned men with prostate cancer to receive immediate prostatectomy or “active surveillance” (aka watchful waiting). The surgery increased survival only for men, age 65 and younger. (To see how modest the survival benefit is even for younger men, click here for results from two 2009 studies.)

Also at issue is the PSA level at which a biopsy is recommended. The men treated aggressively in this study had “a PSA threshold below 4.0 ng/mL.” At a time when some researchers are arguing for lowering this threshold even further, Shao and colleagues made it clear that—given their findings—this would only make a bad situation worse. “Lowering the biopsy threshold but retaining our inability to distinguish indolent from aggressive cancer might increase the risk of overdiagnosis and overtreatment.”

The study was funded by the National Cancer Institute, the Cancer Institute of New Jersey, and the Robert Wood Johnson Foundation.

For more information
Go to the prostate cancer section of the National Cancer Institute’s database to read about screening, treatment options, and active surveillance, which describes the most conservative option of no treatment. This is a remarkably honest source of information. Read both the patient and professional versions.

To learn about the inappropriate use of androgen deprivation therapy for men with early-stage prostate cancer, click here.

Maryann Napoli, Center for Medical Consumers(c)