1. Prostate-specific antigen (PSA) is one of the few molecular markers routinely used in the diagnosis, risk determination and monitoring of the outcome of a common tumor. 2. PSA is prostate-specific rather than prostate cancer-specific. Benign prostate disease often results in elevated serum PSA, and most men with elevated PSA do not have prostate cancer. 3, PSA can effectively distinguish different prostate cancer stages: PSA values are higher in patients with limited (early) prostate cancer than in non-cancerous patients, PSA correlates with the stage and grade of limited prostate cancer, and PSA is higher in metastatic (advanced) prostate cancer than in limited (early) stage. 4. The risk of recurrence after treatment is increased in patients with high PSA at initial treatment. 5. After radical prostate cancer resection, PSA is a sensitive indicator of postoperative recurrence, but after radiotherapy, PSA is not as sensitive in predicting post-treatment recurrence. 6.PSA value before the age of 50 is an important indicator to predict the occurrence of prostate cancer in the future (even 25 years later). 7. The application of PSA and rectal examination (DRE) can diagnose prostate cancer early. The use of PSA as a screening tool may lead to “overdiagnosis”.