A new test for prostate cancer that measures levels of prostate specific antigen (PSA) as well as six specific antibodies found in the blood of men with the disease is more sensitive and more specific than the conventional PSA test used today, according to a new study.
Researchers at the University of California Los Angeles (UCLA; USA) developed the new test, called the A+PSA assay, which checks simultaneously for PSA and antibodies to six prostate-cancer associated antigens in a single reaction test done in a laboratory. The six specific prostate-cancer associated antigens include NY-ESO-1, SSX-2,4, XAGE-lb, AMACR, p90 and LEDGF, which are found predominantly in patients with prostate cancer and not in benign prostate conditions. The new test takes about two hours, similar to the PSA test.
The test results in an index used to diagnose prostate cancer, with a score of 0-0.5 indicating a benign result and 0.5-1 indicating the presence of cancer. In the new test, sensitivity--the percentage of men with prostate cancer who were correctly identified as having a malignancy--was 79%, compared to the 52% found in PSA testing. Specificity--the percentage of healthy men who were correctly identified as not having prostate cancer--was 84%, compared to the 79% found when testing for PSA alone. Additionally, while the rate of false-positives using conventional PSA testing is 21%, the new A+PSA assay delivers a false-positive rate of 16%. The study was published in the May 2011 issue of Translational Medicine.
"Science has improved so much since the PSA test was developed and I think it's time for a more specific and sensitive test to be developed," said senior author Gang Zeng, MD, PhD, an associate professor of urology. "I think we have a test that has great potential to improve the diagnosis of prostate cancer. I knew it would be better than the classic PSA test, but I was amazed at how much better it really was in this study."
"While measuring PSA is useful in identifying men with prostate cancer, some men with prostate cancer have a normal PSA level and small elevations in PSA above normal may be produced both by prostate cancer as well as an enlarged but benign prostate," added coauthor associate professor of urology Allan Pantuck, MD, MS. "Combining PSA with a panel of tests that measure an individual man's anticancer immune response may better identify who has prostate cancer and who can be spared an unnecessary invasive biopsy."
The conventional PSA test for prostate cancer has been used for nearly 30 years and is not specific enough in delineating between malignancies and nonmalignant diseases of the prostate, such as benign prostatic hyperplasia (BPH), an enlarging of the prostate common in aging men that increases PSA levels.
University of California Los Angeles