biomarker

A biomarker, or biological marker, is a measurable characteristic that indicates a biological state, condition, or process. Biomarkers can be molecular, genetic, histologic, radiographic, or physiologic, and they are used to quantify health-related variables, detect disease, monitor progression, or assess responses to treatment.

Biomarkers are commonly categorized by their clinical purpose. Diagnostic biomarkers help establish the presence of a disease. Prognostic biomarkers provide information about the likely course of a disease independent of treatment. Predictive biomarkers forecast how well a patient may respond to a particular therapy. Pharmacodynamic biomarkers reflect a biological response to a drug, while pharmacokinetic biomarkers relate to drug exposure. Surrogate endpoints are biomarkers intended to substitute for clinical outcomes in trials. Examples include troponin as a marker of heart injury, C-reactive protein as an inflammation marker, HbA1c for long-term glucose control, PSA for prostate cancer risk, and BRCA1/2 status for hereditary cancer risk; while imaging biomarkers such as certain MRI findings can indicate tissue changes.

In medicine and research, biomarkers support screening, risk assessment, diagnosis, prognosis, and monitoring of disease or treatment effects. They are central to personalized or precision medicine, guiding decisions about therapies and enabling stratification in clinical trials. In drug development, biomarkers can serve as endpoints or as companion diagnostics that determine eligibility for a therapy.

Validation and limitations are essential. Analytical validity concerns the accuracy of the measurement; clinical validity relates to the association with disease; clinical utility concerns whether use of the biomarker improves health outcomes. Challenges include standardization, reproducibility, pre-analytical variability, and regulatory requirements to demonstrate safety, efficacy, and benefit.