Prostate-specific antigen test

Prostate-specific antigen (PSA), also known as gamma-seminoprotein or kallikrein-3 (KLK3), is a glycoprotein enzyme encoded in humans by the KLK3 gene. PSA is a member of the kallikrein-related peptidase family and is secreted by the epithelial cells of the prostate gland. PSA is produced for the ejaculate, where it liquefies semen in the seminal coagulum and allows sperm to swim freely. It is also believed to be instrumental in dissolving cervical mucus, allowing the entry of sperm into the uterus. PSA is present in small quantities in the serum of men with healthy prostates, but is often elevated in the presence of prostate cancer or other prostate disorders. PSA is not a unique indicator of prostate cancer, but may also detect prostatitis or benign prostatic hyperplasia. Clinical practice guidelines for prostate cancer screening vary and are controversial due to uncertainty as to whether the benefits of screening ultimately outweigh the risks of overdiagnosis and over treatment. In the United States, the Food and Drug Administration (FDA) has approved the PSA test for annual screening of prostate cancer in men of age 50 and older. The patient needs to be informed of the risks and benefits of PSA testing prior to performing the test (see below). PSA levels between 4 and 10 ng/mL (nanograms per milliliter) are considered to be suspicious and consideration should be given to confirming the abnormal PSA with a repeat test. If indicated, prostate biopsy is performed to obtain tissue sample for histopathological analysis. In the United Kingdom, the National Health Service (2018) does not mandate, nor advise for PSA test, but allows patients to decide based on their doctor's advice. As of 2018, the UK National Health Service did not offer general PSA screening, for similar reasons. While PSA testing may help 1 in 1,000 avoid death due to prostate cancer, 4 to 5 in 1,000 would die from prostate cancer after 10 years even with screening. This means that PSA screening may reduce mortality from prostate cancer by up to 25%. Expected harms include anxiety for 100 – 120 receiving false positives, biopsy pain, and other complications from biopsy for false positive tests. Of those found to have prostate cancer, frequent overtreatment is common because most cases of prostate cancer are not expected to cause any symptoms. Therefore, many will experience the side effects of treatment, such as for every 1000 men screened, 29 will experience erectile dysfunction, 18 will suffer urinary incontinence, 2 will have serious cardiovascular events, 1 will suffer pulmonary embolus or deep venous thrombosis, and 1 perioperative death. Since the expected harm relative to risk of death are perceived by patients as minimal, men found to have prostate cancer usually (up to 90% of cases) elect to receive treatment. Men with prostate cancer may be characterized as low-, intermediate-, or high-risk for having/developing metastatic disease or dying of prostate cancer. PSA level is one of three variables on which the risk-stratification is based; the others are the grade of prostate cancer (Gleason grading system) and the stage of cancer based on physical examination and imaging studies. D'Amico Criteria for each risk category are as follows: Given the relative simplicity of the 1998 D'Amico criteria (above), other predictive models of risk stratification based on mathematical probability constructs exist or have been proposed to allow for better matching of treatment decisions with disease features.Studies are being conducted into the incorporation of multiparametric MRI imaging results into nomograms that rely on PSA, Gleason grade and tumor stage. PSA levels are monitored periodically (e.g., every 6–36 months) after treatment for prostate cancer - more frequently in patients with high-risk disease, less frequently in patients with lower-risk disease. If surgical therapy (i.e., radical prostatectomy) is successful at removing all prostate tissue (and prostate cancer), PSA becomes undetectable within a few weeks. A subsequent rise in PSA level above 0.2 ng/mL L is generally regarded as evidence of recurrent prostate cancer after a radical prostatectomy; less commonly, it may simply indicate residual benign prostate tissue.