Biomarkers

Biomarkers are measurable indicators of a biological state or condition. They can be molecular, histologic, radiographic, or physiologic in nature and are used to characterize normal biological processes, pathogenic processes, or responses to a therapeutic intervention. Biomarkers are found in body fluids such as blood and urine, in tissues, or in imaging studies, and may be used alone or in panels to improve diagnostic or prognostic accuracy.

Common biomarker categories include diagnostic biomarkers that indicate the presence of disease (for example, troponin for myocardial injury, prostate-specific antigen for prostate cancer risk, HbA1c for longstanding glucose control), prognostic biomarkers that provide information about disease outcome independent of treatment, and predictive biomarkers that forecast response to a specific therapy (such as EGFR mutations predicting response to tyrosine kinase inhibitors in lung cancer, or BRCA mutations guiding PARP inhibitor use). Pharmacodynamic and surrogate biomarkers monitor biological responses to treatment or substitute for clinical endpoints in trials. Imaging biomarkers, like 18F-FDG uptake on PET scans, also play a key role.

Biomarkers support clinical decision making, disease monitoring, and risk stratification, and they are central to drug development and personalized medicine. In research, they help identify patient subgroups, track target engagement, and accelerate evaluation of new therapies. They may be used as surrogate endpoints in trials, potentially shortening study durations when validated to predict meaningful clinical benefit.

Validation and regulation require demonstrating analytical validity, clinical validity, and clinical utility. Analytical validity assesses the reliability and reproducibility of the measurement; clinical validity establishes a proven association with the disease or state; clinical utility shows that use of the biomarker improves patient outcomes. Standards, reproducibility, and standardization of assays are ongoing challenges, along with biological variability, sample handling, cost, and access. Ethical and regulatory considerations also shape biomarker development and deployment.