prostate-specific antigen (PSA) test is a test that measures the level of PSA in the blood. PSA is a substance made mostly by the prostate that may be found in an increased amount in the blood of men who have prostate cancer. The level of PSA may also be high in men who have an infection or inflammation of the prostate or benign prostatic hyperplasia (BPH; an enlarged, but noncancerous, prostate).

A PSA test or a DRE may be able to detect prostate cancer at an early stage, but it is not clear whether early detection and treatment decrease the risk of dying from prostate cancer.

Studies are being done to find ways to make PSA testing more accurate for early cancer detection.

Source:  NCI