Table 1. Definitions

From reference 10.
Biomarker. A biomarker is a biological characteristic that is objectively measured and evaluated as an indicator of normal biological processes, pathogenic processes, or pharmacologic response to therapeutic intervention.
Surrogate end-point marker. A biomarker that is used in substitution for other clinical end points, such as survival.
Tissue marker. A biomarker that is detected in tissue. Typically these are immunohistochemical stains but, more recently, mRNA or protein.
Discovery phase. The initial investigations to identify potential biomarkers worthy of further study.