PSA, also known as prostate-specific antigen, is a chemical substance synthesized and released by the prostate cells in men. PSA is a tumor marker for prostate cancer, and can be elevated in prostate cancer as well as benign diseases such as prostatitis and enlarged prostate. About 60%-90% of patients with prostate cancer have a significantly elevated total PSA; about 14% of patients with benign prostate diseases such as prostatitis and prostate enlargement have a mildly elevated total PSA.