Improvements Made to Prostate Cancer Test

The blood test accurately identified men with prostate cancer, particularly those with the aggressive form of the disease and substantially reduced false positives compared to the two currently available commercial prostate-specific antigen (PSA) tests.

A study carried out by scientist at Northwestern University, (Evanston, IL, USA), followed male patients from 10 different sites and tested their blood for the presence of Pro-PSA. Immunoassays with high specificity for pro-PSA forms were used to study 1,091 retrospective serum specimens, including 555 men with 2 ng/mL - 4 ng/mL and 536 patients with 4 ng/mL - 10 ng/mL PSA. The participants were enrolled in prostate cancer screening studies, and they had undergone prostate biopsy. The Pro-PSA test measures a more specific PSA subform called [-2] Pro-PSA. The test becomes even more accurate when its results are analyzed with a mathematical formula that provides an overall Prostate Health Index. The formula divides the Pro-PSA number by the free-PSA and then the quotient of the two is multiplied by the square root of the total PSA.

The results showed the new screening test, is particularly useful for patients with a normal prostate examination whose PSA is between 2 ng/mL - 10 ng/mL, a range considered the diagnostic gray zone because most men with higher levels have prostate cancer and most men with lower levels do not. The logic behind the formula is that the higher the Pro-PSA and the total PSA and the lower the free-PSA, the more likely the patient has aggressive prostate cancer. In the 2 ng/mL - 4 ng/mL PSA range the ratio of pro- to free-PSA, using a cutoff of 1.8% for recommending prostate biopsy detected 90% of cancers, including 16 of 16 extracapsular tumors and 28 of 29 tumors with a pathology Gleason score of seven or greater, while avoiding 19% of unnecessary biopsies.

William Catalona, MD, the lead investigator, said, "This new test is more specific and accurate than the currently available blood tests for early prostate cancer detection. This will focus on the detection of more life-threatening prostate cancers and reduce unnecessary biopsies in men 50 years of age and older." The study was published in the May 2011, in the Journal of Urology.

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