A new test based on prostate-specific antigen (PSA) called the Prostate Health Index (PHI) promises to predict more accurately the likelihood of positive prostatic biopsies in patients with PSA levels between 4-10. Moreover, it claims to predict the possibility of high grade prostate cancer better than currently used values. The PHI was approved by the FDA in June of 2012 and has been available since later that year. Clinical data was presented at the AUA (American Urological Association) in 2013.
PHI is a mathematical formula that combines total PSA, free PSA and (-2) proPSA. Free PSA is the prostate specific antigen not bound to other proteins, and the proPSA is a subcategory of free PSA estimated to be 2.5 times specific in detecting prostate cancer in patients than a PSA screening. The PHI combines the 3 blood serum tests – PSA, free PSA and p2PSA – into a single calculation with a mathematical formula: (p2PSA/free PSA) x √total PSA.
The test is simple and inexpensive and has performed better than its components individually. It seems that it has even outperformed the new antigen marker tests like PCA3 and other biomarkers.
The researchers found:
- At 90 percent sensitivity, the specificity of PHI was 31.1 percent, compared to 19.8 percent for %fPSA (p=0.024) and 10.8 percent for PSA (p<0.001).
- At a moderate to high PHI range of 27 to 55, the probability of cancer varied from 9.8 to 50.1 percent and the probability of clinically significant cancer extended from 3.9 to 28.9 percent.
- At a PHI level of 27, which is the 90 percent sensitivity cut-point, 18.8 percent of men could have been spared from undergoing prostate biopsy or over-diagnosis of non-aggressive disease.
Using a PHI level of 27 for selecting men for prostate cancer biopsy, when PSA is 4 to 10 ng/ml, can decrease unnecessary biopsies and reduce over-detection in indolent prostate cancer.