Prostate specific antigen (PSA) is a protein produced by the cells of the prostate gland. PSA is present in small quantities in the serum of normal men, and is often elevated in the presence of prostate cancer and in other prostate disorders. A blood test to measure PSA is the most effective test currently available for the early detection of prostate cancer. Higher than normal levels of PSA are associated with both localized and metastatic prostate cancer (CaP).

Prostate specific antigen (PSA), also known as kallikrein III, seminin, semenogelase, γ-seminoprotein and P-30 antigen) is a glycoprotein manufactured almost exclusively by the prostate gland; PSA is produced for the ejaculate where it liquifies the semen and allows sperm to swim freely. It is also believed to be instrumental in dissolving the cervical mucous cap, allowing the entry of sperm.