Prostate-Specific Antigen (PSA) is a protein produced by cells in the prostate gland, which is located below the bladder in men. PSA is primarily found in semen, but small amounts can also be detected in the blood. It plays a role in liquefying semen, helping sperm to swim more freely. Doctors often measure PSA levels through a blood test to screen for prostate cancer or other prostate-related conditions. Elevated PSA levels can indicate potential issues, but they are not definitive for cancer, as other factors like prostatitis or benign prostatic hyperplasia can also raise PSA levels.