Clinical Significance

PSA is a single-chain polypeptide containing 237 amino acids. It belongs to the serine protease family with tissue-specific chymotrypsin-like action. It can decompose the main gelatinous protein in semen and has the effect of diluting semen. PSA is synthesized in both normal and cancer-like epithelial cells. An inactive zymogen (proPSA) is initially secreted into the prostate duct, and the zymogen cleaves 7 amino acids at the amino terminus to form an active prostate-specific antigen. Most of the prostate-specific antigens entering the blood circulation are rapidly combined with proteolytic enzyme inhibitors, mainly α-1 antichymotrypsin (ACT) and α-2 macroglobulin (MG), and some are inactivated by proteolytic enzymes. exist in a free state.
PSA is tissue-specific and only exists in the cytoplasm of human prostate acinar and duct epithelial cells, and is not expressed in other cells. Prostatitis, benign prostatic hyperplasia, and prostate cancer can all lead to elevated total PSA (tPSA) levels [free PSA (fPSA) plus composite PSA].
In prostate cancer patients, the vast majority of PSA is combined, and the ratio of fPSA/tPSA is lower than that of normal people or patients with benign prostatic hyperplasia. Therefore, for men with abnormally elevated tPSA, detecting fPSA and calculating the ratio of fPSA to tPSA can improve the specificity of screening and diagnosing prostate cancer.

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