companion diagnostic

{{short description|Therapeutic drug diagnostic test}}

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A companion diagnostic (CDx){{Cite news|url=https://www.clinicalomics.com/articles/cancer-cdx-collaboration-brings-foundation-medicine-and-pfizer-together/1433|title=Pfizer Taps Foundation Medicine for CDx Development|last=|date=16 January 2018|work=Clinical OMICs|access-date=19 January 2018}} is a diagnostic test used as a companion to a therapeutic drug to determine its applicability to a specific person.{{cite web|title=Companion Diagnostics |url=https://www.fda.gov/MedicalDevices/ProductsandMedicalProcedures/InVitroDiagnostics/ucm407297.htm |archive-url=https://web.archive.org/web/20140803224157/http://www.fda.gov/MedicalDevices/ProductsandMedicalProcedures/InVitroDiagnostics/ucm407297.htm |url-status=dead |archive-date=August 3, 2014 |publisher=FDA|accessdate=26 September 2016|format=Page Last Updated 07/14/2016}}

Companion diagnostics are co-developed with drugs to aid in selecting or excluding patient groups for treatment with that particular drug based on their biological characteristics that determine responders and non-responders to the therapy.{{cite journal|last1=Trusheim|first1=MR|last2=Burgess|first2=B|last3=Hu |first3=SX|last4=Long|first4=T|last5=Averbuch|first5=SD|last6=Flynn|first6=AA|last7=Lieftucht|first7=A |last8=Mazumder|first8=A|last9=Milloy |first9=J|last10=Shaw|first10=PM|last11=Swank|first11=D|last12=Wang |first12=J|last13=Berndt|first13=ER|last14=Goodsaid|first14=F|last15=Palmer|first15=MC|title=Quantifying factors for the success of stratified medicine |journal=Nature Reviews. Drug Discovery|date=31 October 2011 |volume=10|issue=11|pages=817–833|doi=10.1038/nrd3557|pmid=22037040|s2cid=2079294}}{{Cite book |last=Kim|first=Il-Jin |url=https://books.google.com/books?id=wuOLDwAAQBAJ&q=Companion+diagnostic&pg=PT144 |title=Companion Diagnostics (CDx) in Precision Medicine|date=2019-03-06|publisher=CRC Press|isbn=978-1-000-00721-3}}

Companion diagnostics are developed based on companion biomarkers, biomarkers that prospectively help predict likely response or severe toxicity.{{cite journal|last1=Duffy|first1=MJ |last2=Crown|first2=J |title=Companion biomarkers: paving the pathway to personalized treatment for cancer |journal=Clinical Chemistry|date=October 2013|volume=59|issue=10|pages=1447–1456|pmid=23656699 |url=http://clinchem.aaccjnls.org/content/59/10/1447.long|doi=10.1373/clinchem.2012.200477|doi-access=free}}

For example, there is an automatic immunohistochemistry staining machine for microscopy slides to highlight HER2 expression. This machine is classified by the U.S. Food and Drug Administration (FDA) as a companion diagnostic device for the drug trastuzumab which works on tumors that over-express HER2.{{cite web|url=https://www.fda.gov/medical-devices/in-vitro-diagnostics/list-cleared-or-approved-companion-diagnostic-devices-in-vitro-and-imaging-tools|archive-url=https://web.archive.org/web/20210413055233/https://www.fda.gov/medical-devices/in-vitro-diagnostics/list-cleared-or-approved-companion-diagnostic-devices-in-vitro-and-imaging-tools|url-status=dead|archive-date=April 13, 2021|title=List of Cleared or Approved Companion Diagnostic Devices (In Vitro and Imaging Tools)|website=United States Food and Drug Administration (FDA)|date=2023-05-09}}