What are biomarkers?
OBJECTIVE
This article provides working definitions and a conceptual framework to understand the roles of biomarkers in clinical research.


RESULTS
The definitions of the terms discussed in this article--medical signs, symptoms, biomarkers, surrogate endpoints, clinical endpoints, validation--are still under discussion, as are their relationships to each other, but broad consensus has developed in the past decade and a half about the necessity of distinguishing between, in particular, surrogate and clinical endpoints.


CONCLUSIONS
This article outlines the major definitions of the key terms in this field and considers select cases in which misunderstandings about the terms led to flawed research conclusions.
Strimbu
Kyle
K
Division of Clinical Research, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland 20892, USA.
Tavel
Jorge A
JA
D015415:Biomarkers; D035843:Biomedical Research; D003933:Diagnosis; D006801:Humans; D015203:Reproducibility of Results
D015415:Biomarkers