Researchers at Duke University have discovered why blood levels of prostate-specific antigen (PSA) go up as prostate cancer takes hold in the body.

Published in the Journal of Biological Chemistry, their results suggested that the interaction of antibodies in the blood with cancer cell receptors stimulates the production of PSA, which in turn encourages more cancer growth.

In particular, the team found that the alpha2-macroglobulin antibody reacts with a receptor called the GRP78.

It is this interaction that creates PSA.

High levels of PSA are a relatively good indicator that a man has prostate cancer, although health experts agree that further tests are usually needed to confirm this diagnosis.

According to the National Cancer Institute (NCI), a PSA blood-serum test combined with a digital rectal exam may help men over the age of 50 detect prostate cancer earlier.

However, researchers caution that normal do not necessarily indicate that a patient is cancer-free.

Approximately 15 percent of men diagnosed with prostate cancer have normal , the NCI reports.