What is a Liquid Biopsy?

The term 'liquid biopsy' is gaining traction in the oncology community. Learn what it is and how it can benefit patients.

In a traditional biopsy, some amount of tissue is removed from the patient, properly prepared, and then examined under microscope by a pathologist. This is often done in order to determine whether the patient has cancer, what type of cancer it is, and often, the grade or aggressiveness of the cancer.

In lymphoma, an excisional biopsy-- in which an entire, affected lymph node is removed for pathological examination-- is considered the only type of biopsy fit for reaching an initial diagnosis. The advent of the liquid biopsy has not changed this, because the liquid biopsy is used at a different stage of the treatment process.

What is a liquid biopsy?

From the perspective of a patient, there is a big difference between an excisional biopsy and a liquid biopsy. The excisional biopsy is a surgical procedure, bringing with it all the demands of any such procedure; the liquid biopsy is just your standard blood draw.

To reiterate, undergoing a liquid biopsy requires nothing more from the patient than your standard blood draw. The 'heavy lifting' is done in the lab.

There, health care professionals examine the plasma in the patient's blood. Using highly sensitive tests, they can find what are known as tumor markers in the plasma-- circulating tumor DNA (ctDNA). By measuring the levels of this ctDNA detected in the plasma, they are able to predict whether or not a patient is likely to experience a relapse of their cancer.

Will liquid biopsies replace standard biopsies?

The answer to this question is no. Each biopsy is carried out at different times in the treatment process and for different reasons.

Currently the usefulness of liquid biopsies is limited to patients who have already finished treatment. Typically, once treatment has finished for many patients with aggressive B-cell diseases like diffuse large B-cell lymphoma, they undergo routine imaging such as PET/CT scans every three or six months for a set period of time to see if their cancer remains in remission or if it comes back (relapses). While there is some debate about the value of this routine imaging, there is no debate about the fact that undergoing so much imaging is dangerous to the health of the patient.

This is where the liquid biopsy becomes potentially so valuable. It is a noninvasive technique that could replace routine imaging for lymphoma patients who have finished treatment. Instead of having a CT scan, they might simply need to have blood drawn.

Why won't liquid biopsies replace standard ones?

When a patient is suspected of having lymphoma, they undergo a surgical biopsy, where a lymph node is excised (removed) for examination. The pathologist not only views the lymph node under a microscope, he or she also performs a number of lab tests on the sample, all in an effort to reduce the diagnosis from something general like 'suspected lymphoma' to something highly specific like 'Germinal Center B-Cell-like Diffuse Large B Cell Lymphoma.'

Also, in order to determine whether or not a lymphoma is aggressive, a pathologist must be able to see the lymphoma cells within the context of healthy tissue. The excisional biopsy provides this.

So to recap: a liquid biopsy is performed after a patient has 1) been diagnosed with an aggressive B-cell lymphoma by standard biopsy, 2) undergone a full treatment regimen. The purpose of the liquid biopsy is to determine how effective the treatment regimen was, and to help predict whether or not a patient will experience a relapse. The hope is that liquid biopsies can be proven to be sensitive and accurate enough to replace routine imaging for patients who are post-treatment.

Sources:
National Cancer Institute
Noninvasive monitoring of diffuse large B-cell lymphoma by immunoglobulin high-throughput sequencing
Large B-cell Lymphoma: Is the Future Written in the Blood?

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