Biomarker

Definition

A biomarker is a biological characteristic — such as a blood protein, enzyme, hormone level, genetic variant, imaging finding, or cellular change — that objectively indicates the presence of disease, disease severity, treatment response, or risk of future disease development. Biomarkers are used in clinical research and medical practice for diagnosis, prognosis, risk stratification, and treatment monitoring. Common biomarkers include blood glucose (indicating diabetes status), cholesterol levels (indicating cardiovascular risk), and tumour markers such as PSA (prostate-specific antigen). For peptide research, biomarkers are commonly used to assess treatment effects: for example, in studies of GLP-1 agonists, researchers measure HbA1c (three-month average blood glucose), body weight, and markers of appetite/satiety as biomarkers of treatment effect. Surrogate biomarkers (biomarkers believed to predict clinical benefit but not directly measuring clinical benefit) are sometimes accepted by regulators as primary endpoints in clinical trials, particularly when clinical endpoints would require long-term follow-up. However, surrogate biomarkers require strong evidence that they reliably predict true clinical benefit.

Biomarkers can be classified as diagnostic (indicating disease presence), prognostic (predicting future disease or outcomes), predictive (predicting treatment response), or monitoring biomarkers (tracking disease status or treatment effect). Different biomarkers serve different purposes. For peptide research, biomarkers are valuable because they provide objective, measurable indicators of effect that can be assessed relatively quickly, without waiting for long-term clinical outcomes. For example, in GLP-1 agonist trials, HbA1c response (a biomarker of glycaemic control) is measured after weeks or months, providing evidence of efficacy much faster than waiting to observe reduction in cardiovascular events (which takes years).

The use of biomarkers in clinical trials requires careful interpretation. A biomarker may change in response to treatment (a 'responsive' biomarker), but this does not necessarily prove that the biomarker change translates to clinical benefit for the patient. This is why surrogate biomarkers are more controversial than direct clinical endpoints. Regulatory agencies are increasingly cautious about approving drugs based primarily on surrogate biomarker endpoints; they prefer evidence that the biomarker change predicts true clinical improvement.