PSA, also known as prostate-specific antigen, is a substance secreted by the male prostate gland. Serum PSA, or PSA in blood, is significantly elevated in patients with prostate cancer and is a preferred tumor marker for prostate cancer. If the serum PSA is elevated in both total PSA and free PSA, and the ratio of free PSA to total PSA decreases, it indicates prostate cancer. In benign prostate diseases, such as prostatitis and prostatic hyperplasia, a mild increase in total PSA can also be seen. In addition, the serum PSA should be checked before or several days after prostate massage, anal examinations, cystoscopy, etc. and before or several weeks after prostate surgery. This is because the above tests and surgeries can lead to an increase in serum PSA concentration, which can affect the lab results.