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In expanded studies, Early Prostate Cancer Antigen-2 continues to demonstrate high specificity and sensitivity as a serum biomarker for prostate cancer.
At the AUA annual meeting here, they presented results from indirect enzyme-linked immunosorbent assay (ELISA) of serum from groups of men with BPH, chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS), prostate cancer with a PSA <2.5 ng/mL, and prostate cancer with a PSA ≥2.5 ng/mL, as well as in two groups of healthy men with a PSA <2.5 ng/mL or a higher PSA value. Using a cut-off value of >30.0 ng/mL to discriminate men with prostate cancer, the EPCA-2 ELISA assay had a specificity of 94% and a sensitivity of 91% in separating the non-cancer groups from the groups of men with prostate cancer, regardless of PSA level.
"It is estimated that between 1.3 and 1.6 million PSA tests will be done in the U.S. this year to find the approximately 220,000 men with prostate cancer. So there is clearly a need for prostate cancer markers that are more specific than PSA and that can discriminate the more aggressive and less aggressive forms of the disease," said Robert H. Getzenberg, PhD, Donald S. Coffey Professor and director of urology research at Johns Hopkins.
Expressed selectivity in prostate Ca
"Nuclear changes are the hallmark of the cancer cell, and focusing on nuclear matrix proteins facilitated the proteomic analysis to identify a serum biomarker. In a single drop of blood, there are 100,000 different proteins. Looking for a single protein would be like trying to find one book that is out of place in the Library of Congress," Dr. Getzenberg explained.
"The nuclear matrix proteins are low-abundant proteins, representing less than 1% of the total proteins, and so we thought they would represent excellent targets for identifying markers expressed specifically in prostate cancer."
EPCA-2 was identified as being characteristically changed in prostate cancer in initial studies that analyzed nuclear matrix proteins in cancerous and normal prostate tissue. Further tissue studies confirmed that EPCA-2 was very specific for prostate cancer.
Separating tigers from pussycats
Results of initial testing of the serum bioassay, published earlier this year in Urology (2007; 69:714-20), showed it had high sensitivity and specificity. EPCA-2 was found at a level exceeding the cutoff threshold at high rates among men with prostate cancer, but not in those with other types of cancer, BPH, or an elevated PSA with a repeat negative biopsy. That research also showed EPCA-2 was highly accurate in differentiating men with organ-confined disease at surgery from those men with extracapsular prostate cancer.