Multiplex Assay Enhances Prostate Cancer Test

A blood test has been initiated that is more sensitive and specific than the standard Prostate Specific Antigen (PSA) test.

The novel test, known as the A+PSA assay, looked simultaneously for PSA and antibodies to the six prostate-cancer associated antigens in a single reaction test done in a laboratory, similar to the mode by which PSA is measured.

Scientists at the Jonsson Cancer Center (UCLA; University of California, Los Angeles, CA, USA) used blood taken before surgery from 131 patients from UCLA, Japan and France with biopsy-confirmed prostate cancers and compared results to blood taken from 121 men with either benign prostatic hyperplasia (BPH), or prostatitis, an infection or inflammation of the prostate that increases PSA levels. The assay was designed to assess antibodies in the serum against six specific prostate-cancer associated antigens. The peptide epitopes utilized were from the following: cancer/testis antigen 1B, (NY-ESO-1); X antigen family, member 1B, (XAGE-1b); synovial sarcoma X2, (SSX-2, 4); as well as prostate cancer overexpressed antigen alpha-methylacyl-CoA racemase (AMACR); p90 autoantigen; and lens epithelium derived growth factor, (LEDGF). These epitopes were conjugated with seroMAP microspheres, (Luminex Corporation, Austin TX, USA), to allow multiplex measurement of autoantibodies present in serum samples.

The multiplex assay was more sensitive that the standard PSA test as 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. 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. The rate of false positives using conventional PSA testing was 21%, while with the A+PSA assay, the false-positive rate was 16%.

Gang Zeng, PhD, a senior author of the study, said, "Different men may have different levels of the six antibodies or different antibodies all together based on their race, age, and ethnicity." The team intends to conduct a prospective study that would include the racial, ethnic and age information for each man who provides blood. The test could perhaps be altered for men over a certain age if the antibody levels found in their blood vary. African-American men may also have varying levels of the six antibodies. There also are additional antibodies that could be added to the assay that may improve both the sensitivity and specificity of the test. The study was published on April 19, 2011 in the Journal of Translational Medicine.

Related Links:
Jonsson Cancer Center
Luminex Corporation