Wednesday, March 5, 2014

"Pure Custer": our obsession with the flawed PSA test

In the face of accumulating evidence and a U.S. Preventive Services Task Force finding that prostate-specific antigen (PSA) screening for prostate cancer does more harm than good, the most frequent response I hear from physicians who continue to defend the test is that PSA is all we have, and that until a better test is developed, it would be unethical to not offer men some way to detect prostate cancer at an asymptomatic stage. (However, these physicians for the most part don't question the ethics of not offering women screening for ovarian cancer, which a recent randomized trial concluded provides no mortality benefit but causes considerable harms from diagnosis and treatment.)

A few years ago, I read historian Stephen Ambrose's dual biography of Oglala Sioux leader Crazy House and Civil War cavalry general George Armstrong Custer, whose troops were routed by the Sioux at the famous Battle of Little Bighorn in 1876. One premise of the book is that the same aggressive instincts that served Custer so well during the Civil War - to always attack, even when the strength and disposition of his enemy was unknown - became fatal flaws when he became an "Indian fighter." For most of his post-Civil War career, Custer and his men wandered the Great Plains looking for someone to fight, and not particularly caring if the Indians he engaged in battle were actually at war with the U.S. Army. In one telling description of Custer's first major Western engagement, Ambrose writes:

Here was audacity indeed. ... Custer had no idea in the world how many Indians were below him, who they were, or where he was. His men and horses were exhausted. ... He was going to attack at dawn from four directions at once. He had made no reconnaissance, held nothing back in reserve, was miles away from his wagon train, and had ordered the most complex maneuver in military affairs, a four-pronged simultaneous attack. It was foolish at best, crazy at worst, but it was also magnificent and it was pure Custer.

If readers of American Indian descent will kindly forgive my making this analogy with their 19th century ancestors, this passage is strikingly similar to the way we diagnose and manage prostate cancer. The vast majority of American Indians by this time had either signed peace treaties or were content to leave settlers alone. Under pressure to "do something" about a few troublesome tribes, however, the U.S. Army sent the overaggressive Custer out to do battle with whatever "warriors" he could find, assuming that in the process he would either kill, capture, or scare off those who aimed to do them harm.

That's pretty much what we do by deploying the PSA test to screen for prostate cancer. We cast as wide a net as possible, doing harm at every step of the way: false positives, adverse effects of prostate biopsies, and overdiagnosis and overtreatment of abnormal-appearing cells that we identify - usually inaccurately - as potentially lethal. For every man whose life may be extended by treatment, 30 to 50 will be treated for no benefit, and 10 to 20 will sustain permanent physical harm. And our continuing obsession with this flawed screening test not only flies in the face of evidence, it's pure Custer.


This post first appeared on Common Sense Family Doctor on November 18, 2011.

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