Science in Plain Language: What is a Biomarker?

Sam Westreich, PhD
Feb 4, 2019 · 6 min read
Biomarker: seems important, but what is it? (Image source:

In medicine and biological research, we hear a lot about “biomarkers.” Articles in the Health section of newspapers, both in print and online, exclaim about the discovery of new biomarkers. I often finish the article feeling like someone just stumbled upon some sort of mystical potion, a mysterious compound that will magically fix a deadly disease.

Biomarkers often make the news as a science buzzword. (Image source: Google)

Even at my job (which, admittedly, is a biotechnology focused startup and thus squarely in this realm), I hear the term “biomarker” being thrown around on a near-daily basis. Biomarkers can make a company started in someone’s garage worth millions of dollars, can mean the difference between catching a disease or dying from it — or can bring down a mighty giant, like what happened to the blood-testing company Theranos.

But what is a biomarker? Why do we care about them, and what makes them so valuable?

The short answer: “A biomarker is anything that can be used as an indicator of a particular disease state[.]” -Wikipedia

What about a longer answer?

What is a biomarker?

Drawing blood is a common way to test for biomarkers. Photo by LuAnn Hunt

The longer answer is that a biomarker is a very broad term for something we can test to confirm the presence or absence of a disease. There are two very broad categories of biomarkers:

Molecular biomarkers can include:

Because “biomarker” is such a broad term, there are many different tests to look at them. For a DNA biomarker, for example, a doctor might rub a swab on the inside of your cheek to collect some of your cells. That swab goes to a lab, which can extract the DNA from the cells on the swab and test to see whether you may have a specific mutation.

For an imaging biomarker, a doctor will probably refer you to a specialist for testing. Tests like X-rays, CT scans, PET scans, MRI scans, and other imaging tests will look for imaging biomarkers. These biomarkers might be smudges in a patient’s lungs that could indicate a cancerous tumor.

Many molecular biomarkers are found in blood, including antibodies that are used to detect certain diseases, glucose levels used by diabetics, cholesterol that can indicate a risk of heart disease, and other important molecules. For these biomarkers, a doctor will usually take a blood sample, which is analyzed in a lab.

By looking at either the presence, absence, or level of one or more biomarkers, a doctor can diagnose a patient with a disease. Does your blood have high levels of glucose? This, combined with other symptoms, may indicate that you have Type II diabetes.

Why are biomarkers so valuable, and why do news articles get so excited over finding new ones?

Researchers prefer to use 3 other categories to sort different biomarkers:

All three of these categories are valuable! Discovering a new biomarker in any of these categories could be a huge step forward for medicine.

Let’s imagine a possible near-future scenario:

Your doctor sits down to walk through some of your results. Photo by rawpixel.

You head into the doctor’s office. “We’ve got your blood work back,” she tells you. “I’ve got some new plans for managing your type II diabetes. If you remember from our previous visit, the predictive biomarkers indicated that a low-carb diet could work well for you. Now that you’ve been on that diet for a while, I can see by your pharmacodynamic biomarkers that your diabetes is under much better control, so we’ll keep it up! We also tested your DNA and saw several mutations that are prognostic biomarkers, indicating you may be at high risk for heart disease, so I’d like to put you on an exercise regimen as well.”

Wow! Thanks to all those biomarkers, your doctor has a great idea of how your disease is being managed and how to keep you healthy in the future!

“You found the next prognostic biomarker for cancer — here’s your annual bonus.” Photo by Sharon McCutcheon.

Of course, each of these biomarkers required a test, which is made by a company and sold to every hospital and laboratory. Those tests are expensive and usually a single company has a monopoly on a test, which means that biomarkers are also worth big money, potentially billions of dollars. The first company to patent a test for a specific disease that uses a specific biomarker gets to claim the lion’s share of that money.

“So, is there a gold rush for biomarkers going on? Are people trying to claim every single marker out there, in hopes that it pays off?”

Well, yes and no.

On one hand, it’s true that finding the right biomarker could pay off, to the tune of a billion-dollar drug. But on the other hand, there are a lot of different biomarkers (seriously, we’re talking about hundreds of thousands to millions of different molecules), and the vast majority of them don’t work — at least, not for the illness you may be considering.

Think of the effort that goes into finding a new drug for a disease like Alzheimer’s. Millions of different biomarkers may be tested against cell models and/or animal models, before picking just a handful that go on to FDA clinical testing. This testing will take up to seven years, tens to hundreds of millions of dollars, and leads to failure in the vast majority of cases.

So most biomarkers don’t pan out — and some of them don’t pan out after hundreds of millions of dollars are spent testing them.

Sum it up for me: what’s a biomarker, and why do we care about them?

A biomarker is a fairly generic term that refers to anything that provides information about a disease or condition. Most of the time, the term refers to a biological molecule that either warns of a medical condition, predicts a condition in the future, or gives feedback about whether the condition is getting better or worse.

Finding biomarkers that more accurately detect and predict disease is a huge goal in today’s medical field, so there’s always a flurry of excitement around the announcement of a new potential biomarker for some disease. Most of these discoveries don’t work all the time, or aren’t as effective as other methods, and end up fizzling. Still, one success can pay for many other failures, so researchers and companies continue testing new biomarkers against many diseases and looking for the magic “crystal ball” that can help us better catch and monitor diseases.

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Observations and analysis from a Silicon Valley microbiome scientist on bacteria, biotech, and scientific career development in the startup world.

Sam Westreich, PhD

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PhD in genetics, bioinformatician, scientist at a Silicon Valley startup. Microbiome is the secret of biology that we’ve overlooked.

Sharing Science

Observations and analysis from a Silicon Valley microbiome scientist on bacteria, biotech, and scientific career development in the startup world.

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