Prostate-specific antigen, or PSA is a glycoprotein that is exclusively synthesised by prostate cells; its purpose is the dissolution of the seminal clot.
This protein passes into the blood in very small quantities, but can be detected with a simple blood test.
PSA values are frequently elevated in men with prostate cancer, so it is considered a tumour marker for this disease. It is very useful for detecting signs of cancer in asymptomatic patients, but non-cancerous growth of the prostate (Benign Prostatic Hyperplasia) or inflammatory processes such as prostatitis can also increase the concentration of PSA.