3. What is a biomarker?
- The drug developer’s ultimate goal is to show benefit in clinical end-points (i.e., how a patient survives, feels and functions).
- A biomarker  is, contradistinction to a clinical end-point, ‘a characteristic that is objectively measured and evaluated as an indicator of normal biological processes, pathogenic processes, or pharmacologic responses to a therapeutic intervention’.
- Using this inclusive definition of biomarkers, even very well established measurements, such as blood pressure, or objective tumor response, are properly described as biomarkers, not clinical end-points.
- Biomarkers can give early readouts, before clinical benefit is evident, and help drug developers identify the best investigational drugs, doses, schedules, combinations, and indications to prioritize. 
- Biomarkers can help predict which patient should receive which drug (stratified medicine or personalized healthcare).
 Biomarkers Definitions Working Group. Biomarkers and surrogate endpoints: Preferred definitions and conceptual framework. Clin Pharm Ther. 2001;69:89-95.
 Qualification of imaging biomarkers for oncology drug development. Eur J Cancer 2012;48(4):409-415.