Prostate-specific antigen: Difference between revisions - Wikipedia

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'''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 [[protease|peptidase]] family and is secreted by the [[epithelium|epithelial cells]] of the [[prostate]] gland. PSA is produced for the [[ejaculate]], where it liquefies [[semen]] in the seminal coagulum and allows [[spermatozoon|sperm]] to swim freely.<ref name="pmid12525533">{{cite journal | vauthors = Balk SP, Ko YJ, Bubley GJ | title = Biology of prostate-specific antigen | journal = Journal of Clinical Oncology | volume = 21 | issue = 2 | pages = 383–91 | date = Jan 2003 | pmid = 12525533 | doi = 10.1200/JCO.2003.02.083 }}</ref> It is also believed to be instrumental in dissolving [[Cervix#Cervical mucus|cervical mucus]], allowing the entry of sperm into the [[uterus]].<ref>{{cite book | title=American Society of Andrology Handbook | chapter=Chapter 8: What is the prostate and what is its function? | chapterurl = http://www.andrologysociety.com/resources/handbook/ch.8.asp | isbn=1-891276-02-6 | editor = Hellstrom WJG | year=1999 | publisher = American Society of Andrology | location = San Francisco}}{{dead link|date=December 2016}}</ref>

PSA is present in small quantities in the [[Blood plasma|serum]] of men with healthy prostates, but is often elevated in the presence of [[prostate cancer]] or other prostate disorders.<ref>{{cite journal | vauthors = Catalona WJ, Richie JP, Ahmann FR, Hudson MA, Scardino PT, Flanigan RC, deKernion JB, Ratliff TL, Kavoussi LR, Dalkin BL | title = Comparison of digital rectal examination and serum prostate specific antigen in the early detection of prostate cancer: results of a multicenter clinical trial of 6,630 men | journal = The Journal of Urology | volume = 151 | issue = 5 | pages = 1283–90 | date = May 1994 | pmid = 7512659 }}</ref> The [[United States Preventive Services Task Force]] (USPSTF, 2012) does not recommend PSA screening for prostate cancer, noting that the test may result in "overdiagnosis" and "overtreatment" because "most prostate cancer is asymptomatic for life" and treatments involve risks of complications including impotence (erectile dysfunction) and incontinence;. The USPSTF concludes "the potential benefit does not outweigh the expected harms".<ref name="urlwww.uspreventiveservicestaskforce.org">{{cite web |url=http://www.uspreventiveservicestaskforce.org/prostatecancerscreening/prostatecancerscript.pdf |title=Talking With Your Patients About Screening for Prostate Cancer |format= |work= |accessdate=2012-07-02}}</ref> the American College of Physicians, American Cancer Society, American Urological Association, US Preventive Services Task Force, and American Society of Clinical Oncology recommend providing supportive information for decision-making about PSA screening.<ref name=Screening>{{cite web |url=https://www.uptodate.com/contents/screening-for-prostate-cancer |title= Screening for prostate cancer | date= 2018}}</ref> PSA is not a unique indicator of prostate cancer, but may also detect [[prostatitis]] or [[benign prostatic hyperplasia]].<ref name="pmid23708103">{{cite journal | vauthors = Velonas VM, Woo HH, dos Remedios CG, Assinder SJ | title = Current status of biomarkers for prostate cancer | journal = International Journal of Molecular Sciences | volume = 14 | issue = 6 | pages = 11034–60 | year = 2013 | pmid = 23708103 | pmc = 3709717 | doi = 10.3390/ijms140611034 }}</ref>

==Medical uses==

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{{main article|Prostate cancer screening}}

The American College of Physicians, American Cancer Society, American Urological Association, US Preventive Services Task Force, and American Society of Clinical Oncology recommend providing supportive information for decision-making about PSA screening.<ref name=Screening/> [[Clinical practice guideline]]s for prostate cancer [[screening (medicine)|screening]] vary and are controversial due to uncertainty as to whether the benefits of screening ultimately outweigh the risks of [[overdiagnosis]] and over treatment.<ref name="Gomella2011">{{cite journal | vauthors = Gomella LG, Liu XS, Trabulsi EJ, Kelly WK, Myers R, Showalter T, Dicker A, Wender R | title = Screening for prostate cancer: the current evidence and guidelines controversy | journal = The Canadian Journal of Urology | volume = 18 | issue = 5 | pages = 5875–83 | date = Oct 2011 | pmid = 22018148 | doi = }}</ref> In the United States, the [[U.S. 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&nbsp;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 (2005) does not mandate, nor advise for PSA test, but allows patients to decide based on their doctor's advice.<ref>{{cite news| url=http://news.bbc.co.uk/2/hi/health/4175856.stm | work=BBC News | title=Doctors warn on ad hoc screening | date=2005-08-23}}</ref>

A review commissioned by the [[United States Preventive Services Task Force|U.S. Preventive Services Task Force]] concluded that "Prostate-specific antigen-based screening results in small or no reduction in prostate cancer-specific mortality and is associated with harms related to subsequent evaluation and treatments, some of which may be unnecessary,"<ref name="urlwww.uspreventiveservicestaskforce.org"/> or more simply, "[t]he potential benefit does not outweigh the expected harms" in patients not already diagnosed or being treated for prostate cancer.