biomarker
Meaning of biomarker: Any measurable signal from the body that stands in for something harder to observe directly.
Definition of biomarker
A biomarker is a measurable feature of the body that indicates what is happening inside it. Most are substances found in blood, urine or tissue, though an imaging finding or a physical measurement can serve the same purpose. Biomarkers are used to detect disease, judge how far it has advanced, predict its course, and track the response to treatment.
What counts as a biomarker?
The word covers far more than laboratory chemistry. Anything measurable, repeatable and tied to a biological state qualifies. A protein released by damaged heart muscle is a biomarker. So is a gene change found in tumor tissue, the amount of sugar bound to hemoglobin, the density of bone on a scan, and blood pressure. What matters is not the kind of measurement but whether the number reliably reflects the thing it is meant to stand for.
What are they used for?
| Purpose | Question it answers | Example |
|---|---|---|
| Diagnostic | Is the disease present | Protein released by injured heart muscle |
| Prognostic | How is it likely to progress | Grade of a tumor on a tissue sample |
| Predictive | Will this treatment work | A receptor or gene change in the tumor |
| Monitoring | Is treatment working | A marker measured at intervals |
Why is a good biomarker hard to find?
A useful marker must change early, change in one direction, and change for one reason. Most candidates fail on the last point. A substance that rises in cancer but also rises in inflammation, pregnancy or kidney disease will produce false alarms. Two measures describe that problem. Sensitivity is how often a test catches genuine disease, and specificity is how often it stays quiet when disease is absent. Raising one usually lowers the other. A marker also has to be measurable in something easy to obtain, which is why blood and urine dominate over tissue that requires a biopsy.
What is a surrogate endpoint?
A biomarker is sometimes used in a trial to stand in for the outcome that actually matters, because waiting for that outcome would take many years. Cholesterol level substitutes for heart attacks, and viral load substitutes for progression of HIV infection. The substitution holds only when the marker lies on the causal path. Drugs have improved a marker while leaving patients no better and occasionally worse, which is why a molecular marker result is treated as evidence about a treatment rather than as proof of it.
Also known as
Used in a sentence
Tumor tissue was sent for biomarker testing to establish whether targeted therapy was an option.
Good to know
A biomarker reflects a process rather than proving a diagnosis, and improving the number does not always mean the underlying disease has improved.
Word origin
Where “biomarker” comes from
The prefix bio- comes from the Greek bios, meaning life; marker is an ordinary English word.