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Companion Diagnostics vs Complimentary Diagnostics

By: Natalie Paskoski, NSH Communications Specialist


You may have heard the term companion diagnostic, but what actually is it, and how do companion diagnostics differ from complimentary diagnostics? A companion diagnostic is a test that is required for a patient to receive a specific drug. The drug says on its label, that the test must be run before it can be given to a patient. The result of the test is essential for the safe and effective use of the corresponding drug.


For example, consider Agilent’s PD-L1 IHC 22C3 pharmaDx. This test is considered a companion diagnostic for treatment with Keytruda, for a few types of cancer, including triple-negative breast cancer, cervical cancer, NSCLC and others (on the Dako Link48 autostainer, if you’re using the Dako Omnis it is only approved at this time for NSCLC). So, in order for a patient to be given Keytruda, a test that is FDA approved as a companion diagnostic test for the drug, such as Agilent’s PD-L1 IHC 22C3 pharmaDx, must be run.


The point of a companion diagnostic test like this, is to make sure that the patient is going to actually benefit from the prescribed treatment. In the PD-L1 example, it is to make sure that there is sufficient expression of PD-L1 in the tumor cells for an immune checkpoint inhibitor drug to be worth administering to the patient. Companion diagnostic tests are essential for effective personalized medicine.


A complimentary diagnostic on the other hand, still provides valuable information about whether or not a treatment might be beneficial, but it is not required for the administration of the drug. For a complimentary diagnostic test, the associated drug is safe and effective for a broader section of patients, as opposed to a companion diagnostic associated drug, which is only intended for patients that meet a specific threshold or result from the test. Complimentary diagnostics might apply to a class of drugs, as opposed to providing guidance on a specific drug alone.


To learn more about companion diagnostics, check out the new HistoHelp episode, AwardsCast: Automation, Standardization, and Validation, featuring Jeremy Johnston, the 2020 recipient of the Excellence in Standardization of IHC award.


References:

https://www.cancernetwork.com/view/fda-approves-pd-l1-ihc-22c3-pharmdx-as-companion-diagnostic-for-pembrolizumab

https://myriad.com/managed-care/bracanalysis-cdx/companion-vs-complementary-diagnostics/

https://www.agilent.com/en-us/pd-l1-ihc-22c3-pharmdx-overview

https://blog.crownbio.com/importance-of-companion-diagnostics

https://www.journalofclinicalpathways.com/article/companion-diagnostics-and-complementary-diagnostics-clinical-practice-better-medicine-or

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4215952/



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