New Test Offers Insight:
Is My Cancer Potentially Life-Threatening?
H. Ballentine Carter, M.D., and colleagues at the Baltimore Longitudinal Study of Aging (BLSA ) coined the term, “PSA velocity.” It’s a way of looking at PSA , not just at one isolated test or another, but at a series of tests, looking not only for changes in the numbers, but at how quickly these changes occur.
Studying blood samples taken over a period of decades from the same group of men, Carter watched what happened to men’s PSA levels, years before prostate cancer was diagnosed. Even when the PSA level was low, he found, if it changed by more than 0.35 ng/ml per year, the man was at risk of developing life-threatening prostate cancer.
More recently, Carter and colleagues at the BLSA found a new way to examine PSA velocity (PSA V). This method, called “PSA V risk count,” predicts a man’s risk of developing life-threatening prostate cancer. To calculate this, they counted the number of times that a man’s PSA V exceeded the threshold value (this is similar to breaking the speed limit in a car); how many times, in other words, his rate of change in yearly PSA levels was higher than 0.4 ng/ml. For example, say a man has two PSA V measurements in a row. If his PSA V both times is less than 0.4 ng/ml a year, his risk count is zero. If only one of the two PSA V measurements exceeds 0.4 ng/ml a year, his risk count is 1, and if both PSA V measurements break the speed limit of 0.4 ng/ml a year, his risk count is 2.
This year, a multi-institutional team of investigators, led by Stacy Loeb, M.D., tested whether the PSA V risk count could help resolve some of the drawbacks associated with prostate cancer screening — namely, unnecessary biopsies and the overdiagnosis of insignificant prostate cancer. In men attending a large prostate cancer screening study led by William J. Catalona, a PSA V risk count of 2 (this would mean a man had PSA V measurements that were greater than 0.4 ng/ml, twice in a row) was associated with an eight-fold higher risk of developing prostate cancer, and a five-times-higher risk of having high-grade disease. “This study showed that, after statistically controlling for age and PSA , the PSA V risk count dramatically improved the ability to predict high-grade prostate cancer,” says Loeb.
“ The PSAV risk count dramatically
improved the ability to predict
high-grade prostate cancer.”
Having multiple PSA tests is essential, she adds, so that a man can develop a PSA history. “When we examine the changes in PSA levels over time, it tells us much more than we can learn from just one PSA measurement. In our study, men with sustained rises in PSA , or a PSA V risk count of 2, were substantially more likely to have prostate cancer, and particularly, to develop life-threatening disease. If 0.4 ng/ ml a year is the ‘speed limit,’ then breaking it on multiple occasions carries greater risk. Compared to traditional PSA screening, this PSA V risk count concept may be useful to reduce the number of unnecessary prostate biopsies and the diagnosis of the slowgrowing, fairly benign prostate cancer that may not need to be treated.”