The Prostate Health Index (phi), a blood test that combines 3 PSA measurements into a single score, improves detection of clinically significant prostate cancer (PCa) and could help decrease the number of unnecessary prostate biopsies, researchers reported.
In a study of 658 men aged 50 years and older with PSA levels of 4–10 ng/mL, Stacy Loeb, MD, of New York University, and colleagues investigated whether phi can improve specificity for detecting clinical significant PCa and reduce PCa over diagnosis. The researchers used the Epstein definition of clinically significant PCa (Gleason score 7 or higher, 3 or more positive cores, and more than 50% involvement of any core).
The test measures total, free, and [-2]proPSA (p2PSA), the latter being an isoform of free PSA identified as the most PCa-specific form found in tumor extracts.
Phi outperformed its individual components in detecting clinically significant PCa, the researchers reported in The Journal of Urology (2015;193:1163-1169). Using a 90% sensitivity cutoff for significant versus insignificant PCa (a phi threshold of 28.6) could potentially avoid 30% of biopsies with indolent or no PCa compared with 21.7% using free PSA alone, the investigators reported.
The new study builds on previous research showing that phi improves specificity and provides a greater net benefit for PCa detection compared with total and percent free PSA, the researchers pointed out.
“Phi is a simple blood test that we recommend for use as part of a multivariable approach to reduce unnecessary biopsies and over diagnosis,” the authors concluded.
Dr. Loeb's group acknowledged some study limitations, including the use of biopsy criteria to define clinical significance. “Although biopsy criteria are frequently used, these end points are not perfect and other factors such as life expectancy also have a key role in defining over diagnosis,” they wrote.
With regard to study strengths, the researchers noted that their study used a prospectively enrolled source population, including a large number of men from multiple centers across the United States.
The study population had a median age of 63 years. Of the 658 men, 324 (49.2%) had PCa detected on biopsy. Among the men with PCa, 52.5% had clinically significant disease and 33.7% had Gleason 7 or higher tumors.
The study was funded by Beckman Counter Inc., of Carlsbad, Calif., which markets the phi test. The test received FDA premarket approved in June 2012 and the company announced the test's availability in the United States in May 2014.
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