The Top 4 Liquid Biopsy Myths

It is now possible to map the genomic makeup of a cancer tumor and identify personalized treatment options with just a simple blood test. Known as “liquid biopsies,” this new breed of testing decreases the need for tumor tissue biopsies that are costly, risky, and painful. It opens a whole new class of diagnostic tests and fuels hopes of better treatment options for patients. However, as with any new and exciting development, it is important to understand that not all liquid biopsies are created equal.

Liquid Biopsy Myth #1

Liquid Biopsies Are Always Non-invasive

The term liquid biopsy can be used for any type of specimen other than tissue — including blood, urine, and cerebral spinal fluid — that can be interrogated regarding the functionality of a cancer tumor. While liquid biopsies are generally considered non‐invasive, any patient who has undergone a spinal tap to collect cerebral spinal fluid would probably not agree. A liquid biopsy can also cover biopsies for hematological cancers, and again, bone marrow biopsies are a far cry from non‐invasive.

Liquid Biopsy Myth #2

All Liquid Biopsies Interrogate the Same Biomarkers

There are two main types of biomarkers interrogated for by liquid biopsies: cell‐free DNA (also known as circulating tumor DNA) and circulating tumor cells (CTCs). Cell‐free DNA are small DNA fragments that are shed by the tumor into the bloodstream. Circulating tumor cells are exactly what the name implies — intact tumor cells in the blood stream. The major difference is that cell‐free DNA is >100 times more abundant in the bloodstream than CTCs. In a 10mL blood sample, you may only find a handful of CTCs at most, whereas with cell free DNA, there are tens to hundreds of genome equivalents that make it easier to test.

Liquid Biopsy Myth #3

All Liquid Biopsies Are Tested the Same Way

All liquid biopsies are not tested in the same way. Comprehensiveness is one differentiating factor. Some liquid biopsies only test for a few specific genomic alterations. In this case it is usually done with “hot spot” testing, which tests 1‐10 specific mutations within the gene. Other liquid biopsies test across the whole exon of the gene to provide a more comprehensive picture.

Liquid biopsy tests also differ in the type of genomic alterations being interrogated. Most only do one or two of the following alterations: single nucleotide variants (SNVs), copy number variants (CNVs), fusions (re‐arrangements), and insertions/deletions (indels). In addition, some liquid biopsy tests are designed for only a specific type of cancer, whereas others are pan cancer.

Liquid Biopsy Myth #4

These Tests are Only Available Today for Research or are Still in Development

Guardant360, the most advanced non‐invasive tumor genomic test, is available today and used on a daily basis for clinical testing of cancer patients. The test features a comprehensive panel of 68 clinically relevant genes including SNVs, CNVs, fusion, and indels. Cell‐free DNA is extracted from blood and sequenced using NGS. This provides broad interrogation across >150,000 bases and not just information across 1‐10 specific mutations.


A Better Way

We refer to Guardant360 as biopsy‐free testing instead of as a liquid biopsy. This is an important distinction, since it is the first and only comprehensive non‐invasive test for tumor sequencing that is currently in clinical use. Mention biopsy in front of a patient and watch the anxiety flicker across their face. A biopsy means pain, a potential long recovery, and an agonizing wait for results. Guardant360 is the antithesis of a biopsy. It involves no pain, no recovery, and delivers results in 14 days or less. Biopsy‐free tests are changing the way physicians look at a patient’s cancer in real time and giving those patients options they have never had access to before.