Setting a “Speed Limit” on PSA


All prostate cancer is the same, and all of it needs to be treated. Right? No! But which prostate cancer is bad, and which cancer is slow-growing, not aggressive, and not likely to cause any trouble? Maybe this is not the right question. Instead, says urologist H. Ballentine Carter, M.D., the Peter Jay Sharp Foundation Scholar, the answer may lie in setting a “speed limit” for PSA.

“Prostate cancer detection has always focused on finding all cancers, regardless of their potential to cause harm,” says Carter, a pioneer in the study of PSA and the clinical definition of “incidental” prostate cancer (very slow-growing cancer that happens to be in the prostate, but doesn’t ever seem inclined to leave it), which is often detected by regular PSA screening and treated needlessly.

“Many investigators are looking for methods of preferentially identifying cancers that are destined to cause harm, as an alternative to detecting all prostate cancers.” But Carter has another idea: A new approach, called “risk count assessment,” which doesn’t look at the cancer itself as much as what it does. His work, done along with colleagues Anna Kettermann, Luigi Ferrucci, Patricia Landis, and Jeffrey Metter, was published in Urology.

Carter’s approach doesn’t look at good vs. bad cancer, but at what the cancer does.

Using data from the Baltimore Longitudinal Study of Aging (BLSA), Carter, along with investigators in the Brady and the National Institute on Aging, has found that “the number of times a man’s PSA exceeds a speed limit is directly related to his risk of having harmful prostate cancer.” This speed limit is also known as PSA velocity — how fast a man’s PSA level changes from year to year.

In this study, the PSA levels of 717 men were followed for between 20 and 30 years; 32 of these men had harmful cancers. Carter looked at how the levels changed over time, and also worked to figure out the proper yearly “speed limit.” How much of a change in PSA is okay? “If the PSA speed limit was 0.4 ng/ml per year,” he reports, “a man who exceeded this limit once had a 15-percent chance of harboring a harmful prostate cancer, and if there were three ‘speeding violations,’ his chance went up to 30 percent. However, if we raised the speed limit to 0.75 ng/ml per year, one violation was associated with about a 20-percent of harmful cancer, and a 60-percent risk of it with three violations.”

The bottom line here, Carter says, is that increases in PSA — no matter how low the actual level is — should be viewed as evidence of the possible presence of a harmful cancer, “especially if the PSA increases occur repeatedly.”

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