PSA is a protein produced by the prostate gland that helps to keep the semen moist.

The level of PSA (prostate specific antigen) in the blood can be raised for various reasons. This includes  massaging the prostate,  (after an examination of the prostate by the doctor) ,benign (non-cancerous) prostatic enlargement, inflammation or infection of the prostate, surgery to the prostate or bladder as well as in cancer of the prostate. Also up to a third of  men with prostate cancer have a normal PSA level, this is more likely if the cancer is very small.

So the PSA level is useful as a way of testing for abnormalities in the prostate but is not specific for cancer. This is one of the reasons why the use of PSA measurement as a means of screening for early prostate cancer remains controversial. For those patients who have proven prostate cancer and a raised PSA level, monitoring the PSA offers a useful way of checking on the progress of the disease and the response to treatment.