companion diagnostic test (kum-PAN-yun DY-ug-NAH-stik …)
A test used to help match a patient to a specific drug or therapy. For example, a companion diagnostic test may identify whether a patient’s tumor has a specific gene change or biomarker that is targeted by the drug. This helps determine if the patient should receive the drug or not. Companion diagnostic tests can also be used to find out whether serious side effects may occur from treatment or how well treatment is working. Most drugs with a companion diagnostic test are cancer drugs that target specific tumor mutations.