also called PSA. A protein made by the prostate gland. Levels of PSA in the blood often go up in men with prostate cancer as well as other conditions. The PSA test is sometimes used to help screen for prostate cancer, and PSA levels are part of what determine the stage of a prostate cancer. The test can also be used to check the results of treatment, to look for possible cancer recurrence, and to help monitor advanced prostate cancer. See also prostate.