|Graphic depiction of risk without or with PSA tests, from|
the Harding Center for Risk Literacy.
This is precisely what happened with prostate cancer in the early 1990s, just after screening tests for prostate-specific antigen (PSA) became widely available. As explained by NIH's Paul Pinsky and colleagues in an article in the New England Journal of Medicine this week, prostate cancer rates rose from 135 (cases per year, per 100,000 men) in 1988 to 220 in 1992, a 63% increase in just four years. Rates slowly dropped after that, but they remained above 150 through 2009.
No one believes that this increase represented an actual increase in the rate of prostate cancer. Instead, it was an increase in the rate of diagnosis, made possible by the PSA test. After this simple blood test became available, millions of men started getting routine PSA testing. The idea was that, because prostate cancer increases the levels of PSA in the blood, this test could detect cancer early, which in turn would save lives.
It hasn't worked out that way. The problem is that, as a large body of evidence has now shown, most prostate cancers are slow-growing, "indolent" tumors that don't kill you, at least not before something else does.
What's worse is that the treatments for prostate cancer have very serious, life-altering side effects. 20-30% of men treated with surgery and radiation suffer from long-term incontinence, erectile dysfunction, or both.
This is especially problematic given that the false-positive rate of PSA testing is as high as 80%. In other words, if your doctor tells you that your test was positive, there's an 80% chance that you don't have cancer. Many men, though, elect for further, much more invasive testing after a positive result, because who can sleep at night without knowing for certain?
But how about the benefits of early detection? Alas, they did not materialize. Very large trials (including the PLCO study, with over 75,000 participants) showed that routine PSA screening did not prevent any deaths. The only study to show any benefit, ERSPC, had serious flaws, as explained by Ian Haines and George Miklos in the Journal of the National Cancer Institute.
Putting all these facts together, the US Preventative Services Task Force concluded that the harms of PSA testing substantially outweigh the benefits, and it recommends, bluntly:
"Do not use prostate-specific antigen (PSA)-based screening for prostate cancer."The American Academy of Family Physicians agrees, stating:
"There is convincing evidence that PSA-based screening leads to substantial over-diagnosis of prostate tumors. Many tumors will not harm patients, while the risks of treatment are significant. Physicians should not offer or order PSA screening unless they are prepared to engage in shared decision making that enables an informed choice by patients."Even the American Urological Association, which strongly opposed the USPSTF recommendation when it first appeared, now recommends against PSA screening except in one age group, men 55-69 years old. The AUA, though, is highly biased in favor of testing, because its members make significant income from PSA tests and the subsequent follow-ups.
Prostate cancer is a very serious disease among older men. According to the American College of Physicians, 1 out of 16 men will receive a diagnosis of prostate cancer in their lifetimes, although only 2.9% will die of it, most of them older than 75. Nonetheless, PSA screening does not help: it carries a significant risk of harm. In this week's NEJM article, Pinsky et al. conclude:
"Under the `first do no harm principle,' it seems reasonable to forgo mass screening as a public health policy at this point."Someday we may have a better test for prostate cancer, but for now, we don't. If your doctor offers you a PSA test, your best response is probably to tell him no thanks.
[Aside: the article in the New England Journal of Medicine was written by scientists from the National Cancer Institute at NIH, yet it's behind a paywall that prevents anyone from reading it without paying a costly fee or an even more expensive subscription to the journal. Why do we have to pay a fee to read work that the taxpayers already paid for?]