Prostate cancer and the PSA test: It’s hard to understand risk

The U.S. Preventive Services Task Force has released new guidelines for prostate cancer screening — urging doctors not to use the popular PSA test to detect the disease.

The new recommendations, which were published in the journal Annals of Internal Medicine on Monday, hardly mark the first time public health officials have called the value of the blood test into question. The first concern is that the test doesn’t actually save lives. The second is that it might cause harm because it ferrets out slow-growing cases of prostate cancer as well as aggressive ones -- leading many men with harmless cases to get unnecessary treatment. Fighting prostate cancer can involve surgery or radiation, and can cause men distress, incontinence and sexual dysfunction, critics of overtreatment say.

But advice against screening can be difficult for physicians and patients to accept, said researchers who study how the public understands health risk.

Julie Downs, director of Carnegie Mellon University’s Center for Risk Perception and Communication, said that patients often think of cancer the same way they think of infectious disease — as a toxin in the body that needs to be expunged, rather than cells gone awry that might best be left alone. Intuitively, it’s hard to regard cancer as a condition you’re more likely to die with than to die from.

“People think, there’s this thing in there, why wouldn’t you want to get rid of it? It doesn’t make sense to say, why don’t you just leave it there,” Downs said.

What’s more, taking a test gives fearful patients a feeling of control, she added. Take away the screening tool and you “take away the one thing I felt I could have done,” she said.

Noel Brewer, an associate professor of health behavior at the University of North Carolina in Chapel Hill and member of the U.S. Food and Drug Administration’s Risk Communication Advisory Committee, compared the phenomenon to riding a roller coaster.

“People love to be scared, and then to feel relieved. That’s what the PSA does,” he said.

Having a cancer diagnosis — even a false one — reinforces patients’ conviction that getting the test was the right thing to do, he said. What, after all, might have happened if I hadn’t found out?

The problem with such reasoning, Downs said, is that it’s impossible to know. When doctors consider the experiences of their own patients, they “see someone who was treated and didn’t get cancer,” she said. “But they don’t see the people who weren’t treated and didn’t get cancer. It’s a biased sample effect.”

The Annals of Internal Medicine offers a guide to the new PSA recommendations for patients here.

The journal has also published reactions to the task force guidelines from American Cancer Society chief medical officer Dr. Otis Brawley and from a team of prostate cancer physicians who write that the recommendations “underestimated the benefits and overestimated the harms of prostate cancer screening.”