Biomarkers in Drug Development

Definition & conceptual foundations

• Definition (FDA-NIH BEST) — A biomarker is a defined characteristic that is objectively measured and evaluated as an indicator of normal biological processes, pathogenic processes, or responses to an exposure or intervention — molecular, histologic, radiographic or physiologic characteristics all qualify.
• The fault line vs a clinical endpoint — A biomarker is NOT an assessment of how a patient feels, functions or survives — that distinction is exactly what separates a biomarker from a clinical endpoint.
• Why they matter in drug development — In clinical medicine biomarkers aid diagnosis, monitoring, efficacy/safety assessment and prognosis; in drug development they add target engagement, proof-of-concept and safety signalling. Rational use raises the probability of programme success, and validated surrogate endpoints enable faster availability of new therapies.
• Historical drivers & a cautionary tale — CAST: antiarrhythmics (encainide, flecainide) suppressed ventricular ectopy (the biomarker) yet increased mortality — biomarker response can be dangerously discordant with outcome. The HIV/AIDS epidemic drove surrogate use (plasma HIV-RNA suppression underpinned accelerated antiretroviral approval). The 2004 FDA "Critical Path" white paper launched the Critical Path Initiative and a formal Biomarker Qualification Program.
• Standardising the language — BEST — The FDA-NIH BEST (Biomarkers, EndpointS, and other Tools) Resource is a harmonised, intentionally "living" glossary defining biomarker/endpoint terms and the hierarchical dependencies among them.