Time Will Tell the Utility of Biomarkers.

A biomarker, such as protein accumulation as an indicator of disease, can be used to predict disease manifestation, determine intervention, and monitor treatment efficacy. Biomarker development frequently focuses on early detection of disease as this is typically considered the only or most pressing need. However, the ideal time point for biomarker use may not always be early in disease but instead, as we will discuss, could be when enough information is available to predict the association between biomarker (protein accumulation) and disease manifestation (symptom severity, progression, prognosis). This Viewpoint highlights the importance of clearly defining the notion of "time" when discussing the development and utility of biomarkers. Using two disease examples, one with a clearly defined starting point (traumatic brain injury) and one with an indistinct starting point (Alzheimer's disease), we explore the concept of timing in biomarker development and utility.