A new urine assay that can detect genetic changes correlated with prostate cancer correctly identified cancer grade in 92% of men with elevated prostate-specific antigen (PSA) levels that had high-grade cancers.1
Despite its common use, the PSA blood test cannot distinguish between low-grade cancer and high-grade cancer. Low-grade cancer can be monitored and does not need active treatment whereas high-grade cancer requires surgery and radiation therapy. Elevated PSA levels are values higher than 4 ng/mL.
The United States Preventive Services Task Force (USPSTF) recommends against PSA-based screening as PSA blood tests generate a large number of false positives. Only approximately 25% of men with elevated PSA levels have prostate cancer.
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This study, published in JAMA Oncology, compared a urine-based gene expression assay with biopsy results from 499 patients whose PSA levels were between 2 ng/mL and 20 ng/mL to train the assay for deriving prognostic scores. Next, researchers validated derived prognostic scores in urine samples from 1064 patients from 22 community practice and academic urology clinics in the United States.
Samples were from participants who did not have indolent prostate cancer, were 50 years or older, and were scheduled for an initial or repeat prostate needle biopsy due to digital rectal examination results and/or PSA levels (limit range, 2.0 to 20.0 ng/mL).
At a derived prognostic score of 15.6, researchers correctly identified the cancer grade as high in more than 90% of men with prostate cancer. In addition, the assay correctly identified the cancer grade as low in 91% of men with the disease. A score above 15.6 predicted high-grade cancer, and a score below 15.6 predicted low-grade cancer.
In 66% of men with low-grade cancer, however, the test incorrectly predicted high-grade cancer. In clinical practice, use of this test would have saved 27% of men from undergoing unnecessary prostate biopsies.
“The test has the potential to be a significant improvement over PSA alone in distinguishing between low- and high-grade prostate cancer, especially in the PSA gray-zone patient,” said James McKiernan, MD, the John K. Lattimer Professor and chair of urology at Columbia University Medical Center and urologist-in-chief at NewYork-Presbyterian/Columbia, New York City, and first author of the study.
“It could reduce hundreds of thousands of invasive biopsies each year. Given the pain and risks associated with performing a prostate biopsy, that’s not a trivial thing.”
This is the only urine-based experiment that does not need a rectal digital examination before collection. Furthermore, the test is easy to integrate into the clinical setting.
Grants from Exosome Diagnostics supported this study.
REFERENCE
1. McKiernan J, Donovan MJ, O’Neill V, et al. A novel urine exosome gene expression assay predicts high-grade prostate cancer at initial biopsy [published online ahead of print March 31, 2016]. JAMA Oncol. doi:10.1001/jamaoncol.2016.0097.
