Biomarker testing is when doctors take samples from your body like blood or saliva and measure specific biological molecules called biological markers or biomarkers for short. These tests may provide useful information about how to treat your cancer. Not all cancers have known biomarkers, so you may not have had biomarker testing before. You may be asked to have further testing if a clinical trial needs information about a particular biomarker for research or to see if you meet the trial eligibility requirements. The trial usually provides financial support for required biomarker testing. Ask your doctor or the trial contact for more information. Use the NCI tool in the lower-right corner to search for terms you are unfamiliar with.