MedWire News: The Prostate Health Index (PHI) is better able to predict the need for biopsy and the likelihood of prostate cancer than the standard prostate-specific antigen (PSA) test in men whose levels are in the so-called "gray area" between 2 and 10 ng/ml, say researchers.
The PSA test, which recommends biopsy at a PSA level of 4 ng/ml or greater, detects significant, curable cancer, but with limited specificity, and can therefore lead to unnecessary biopsy, explains the team.
Indeed, prostate cancer is found in approximately 25% of patients with PSA levels under 10 ng/ml, creating a "diagnostic gray zone," which is important since "most prostate cancer is curable at PSA less than 10 ng/ml while PSA greater than 10 ng/ml often portends advanced disease," observe William Catalona, from Northwestern Feinberg School of Medicine in Chicago, Illinois, USA, and colleagues.
The PHI is a mathematical formula that uses a measurement of a precursor of PSA called [-2]proPSA (p2PSA). p2PSA is found in free PSA (fPSA; serum PSA unbound to proteins), and has been shown in previous studies to improve the specificity of prostate cancer detection relative to free-to-total PSA ratio - another marker of the disease.
Catalona and co-workers analyzed serum samples from 892 men with available biopsy, PSA, and prostate cancer history data, and of whom 430 (48.2%) had prostate cancer. All men had PSA levels between 2 and 10 ng/ml and non-suspicious physical examination results.
PHI scores and p2PSA levels were significantly higher in patients with prostate cancer than those without, while fPSA and free-to-total PSA levels were lower, report the researchers in the Journal of Urology.
Using a sensitivity of 95% in receiver operating characteristic analysis, the PHI had the highest specificity for prostate cancer detection compared with other markers such as; free-to-total PSA, p2PSA, PSA and fPSA, at 16.0% versus 8.4%, 7.6%, 6.5%, and 3.5%, respectively.
Furthermore, the area under the curve score (where a score of 1 indicates perfect discrimination) for PHI was also higher than for each of these other markers, at 0.703 compared with 0.648, 0.615, 0.557, and 0.525, respectively.
When sensitivity was lowered to 90%, the specificity of PHI became significantly greater than that of the other PSA-based prostate cancer markers.
"The logic behind the formula is that the higher the proPSA and the total PSA and the lower the fPSA, the more likely the patient has aggressive prostate cancer," said Catalona.
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