"To screen, or not to screen?" That is the question. Every day, I have conversations behind closed exam room doors about whether or not to do certain tests, and how to find certain diseases before they become serious. The decision to do a PSA, or prostate specific antigen, is probably among the most controversial of these conversations.
For years, and as it turns out, with very little evidence that it actually works, physicians and patients have advocated for this test as a way to screen men for prostate cancer. Cancer is the second leading cause of death among American men, and prostate cancer is the most common cancer, so it goes without saying that screening for it makes sense? Maybe not! The first hint at why routine screening might not make sense lies in the numbers. The while about 138 out of 100,000 American men might develop prostate cancer each year, only 22 out of 100,000 die of the disease. Indeed, the National Cancer Institute shows that an American man has a 16% lifetime risk of developing prostate cancer, and only a 3% chance of dying from it. Some of this discrepancy could be the result of highly effective treatment and cure (in other words, we do a great job of screening and finding early, curable disease). However, a deeper dive into the data reveals this may not be the only factor, and may not even be true!
Autopsy studies show that nearly 2/3 of elderly men die with, not because of asymptomatic prostate cancer. Is it possible that prostate cancer just isn't all that dangerous a disease, and that screening doesn't actually do anything but find a cancer that would never actually kill? A systematic review published in the British Medical Journal in 2010 pooled the results of six randomized controlled trials (the gold standard for medical research) to examine that very question. The results were a bit surprising: PSA screening did not change a man's chance of dying from prostate cancer, though more cancer was found (only 2% more, though). In fact, the screening did not change the man's risk of dying from any cause. Closed case then? Well, almost! In what has become "par for the course" with studies about the PSA, one of those six trials published follow-up data in 2012. It did show a slight reduction in death due to prostate cancer (1.07 deaths per 1000 men screened). However, the risk of dying from any cause was unaffected. Essentially, finding and curing prostate cancer, according to this study, does not change life expectancy.
Thus far, this article has only addressed the benefits, or lack thereof, of the PSA. What are the risks? After all, this is just a blood test. Isn't an unskilled phlebotomist the worst thing that could happen? Not really. Since the day the PSA came out, we've known it has a high false positive rate. Some studies put this rate as high as 75%. In layman's terms, out of four positive PSA tests, only one will turn out to be cancer. How do we know which one? Well, that's where the risk arises. The only true way to tell is by sending all four men for surgical biopsy of the prostate, a procedure which carries the risk of infection and bleeding (around 0.7% which isn't insignificant given the large numbers of men being screened). Other studies show a high rate of lasting psychological harm cause by false positive PSAs. The far greater concern lies in treatment for prostate cancer. Keeping in mind that treatment may not actually change life expectancy according to some of the studies I referenced earlier, the rate of complications from treatment, traditionally removal of the cancerous gland, is fairly large. Thirty-six percent of men will be left with erectile dysfunction. Twenty-eight percent will be incontinent of urine after treatment. This infographic puts the numbers into perspective.
As a result of the confluence of studies, the U.S. Preventive Services Task Force (USPSTF) recommended against routine screening for prostate cancer in men using the PSA. So, I never order the test, right? Wrong! The word "routine" here is an important one, as it was when the USPSTF recommended, to much ado, against routine mammogram in women 40-50 years of age. I still order the test fairly often, but only when there is some factor increasing a man's risk (family history, African-American race, etc.) or after a this long, and relatively complex discussion of risks and benefits have occurred. If you have not had a similar conversation with your physician, I'd encourage you to do so before having the PSA done.
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