Hello. PSA (prostate specific antigen) is the most specific tumor marker of prostate cancer and a serine protease secreted by prostate epithelial cells. Under normal circumstances, there is a barrier between PSA-rich prostatic acinar contents and lymphatic system, which consists of endodermis, basal cell layer and basement membrane. When tumor or other pathological changes break this barrier, the contents of glandular duct can leak into lymphatic system, and then enter blood circulation, leading to the increase of PSA level in peripheral blood. At present, it has been considered that the total serum spa >；; 4.0ng/ml exception, it is recommended to review for the first time.