What is a Biomarker?
The term “biomarker” is composed of “biological” and “marker.” Different disciplines have slightly different definitions for biomarkers, but the general concept is consistent.
The National Institutes of Health (NIH) in the United States defines a biomarker as: “A characteristic that is objectively measured and evaluated as an indicator of normal biological processes, pathogenic processes, or pharmacologic responses to a therapeutic intervention.”
The World Health Organization (WHO) provides a broader definition: “A measurable substance, structure, or process that can be used as an indicator of normal biological processes, pathogenic processes, or pharmacologic responses to a therapeutic intervention.”
In general, biomarkers can refer to a broad subset of medical markers, which are objective indicators of a medical state that can be observed from within or outside a patient. These indicators can be measured accurately and repeatedly. Medical markers are different from medical symptoms, which are signs of health or illness that are perceived by the patient themselves.
A biomarker is a measurable molecular, cellular, or biochemical change that can be used to identify and monitor physiological processes, pathogenic processes, or responses to a therapeutic intervention.
The key point is that biomarkers can not only help diagnose diseases (diagnostic biomarkers) but also help identify potential treatments and track the progression, regression, and outcome of a disease following intervention.
Biomarkers can include carbohydrates, proteins, lipids, genes, DNA, RNA, platelets, enzymes, hormones, and other biomolecules. Any substance that can help identify a disease can be a biomarker, whether it is a change in a metabolite, biological structure, or biological process, or a characteristic.
The Classification of of Biomarkers
- Prognostic Biomarkers: These indicate the likely outcome of a disease in an untreated individual. For example, the presence of a PIK3CA mutation in HER-2 positive metastatic breast cancer is associated with a lower disease-free survival rate.
- Predictive Biomarkers: These identify patients who are likely to respond positively to a specific treatment. For instance, EGFR mutations predict a better response to erlotinib treatment in non-small cell lung cancer.
- Pharmacodynamic Biomarkers: These help determine a drug’s pharmacological action and can indicate whether a treatment is working as intended. For instance, phosphorylated AKT (pAKT) can serve as a pharmacodynamic biomarker for PI3K inhibitors.
- Surrogate Biomarkers: These are similar to predictive biomarkers but are used as a substitute for a clinical endpoint. For example, blood pressure is a surrogate biomarker for heart disease.
In summary, biomarkers are valuable tools in medical research and clinical practice. They can aid in early disease detection, treatment selection, and monitoring of disease progression.