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 men with healthy prostates, but is often elevated in the presence of prostate cancer and in other prostate disorders. A blood test to measure PSA is considered the most effective test currently available for the early detection of prostate cancer, but this effectiveness has also been questioned.
Rising levels of PSA over time are associated with both localized and metastatic prostate cancer (CaP).