Prostate Specific Antigen (PSA) is a protein produced mainly by cells in the prostate gland and can be a useful indicator of prostate cancer. This protein can be found in all males.  In blood, PSA is present both as free PSA and as complexed PSA bound to other blood proteins.

Elevated PSA levels do not always indicate cancer but may be due to an infection of the prostate gland (prostatitis) or benign prostate enlargement.

Ongoing PSA testing can provide important information about the response to therapy and the risk of relapse.