PSA is of great significance for the diagnosis of early asymptomatic prostate cancer. Under normal circumstances, PSA is a serine protease secreted by prostate epithelial cells, a glycoprotein that is directly secreted into the prostatic ductal system. Its normal function is to help hydrolyze and liquefy semen clots, which is related to male fertility. There is a blood epithelial barrier around the normal prostate ductal system, which prevents PSA produced by the prostate epithelium from entering the bloodstream directly, thereby maintaining a low concentration of PSA in the blood. It is generally believed that serum PSA less than 4.0 ng/mL is normal, while PSA greater than 10 ng/mL increases the risk of developing pre adenocarcinoma. When the prostate gland undergoes cancer, it breaks the blood-epithelial barrier, and the cancer secretes more PSA, causing PSA to enter the bloodstream directly. The higher the malignancy of the cancer, the greater the damage to normal prostate tissue, and the higher the serum PSA.