'Liquid biopsies' provide up-to-date info for doctors
Ask the Expert: A blood test known as a "liquid biopsy" is less invasive, less costly and less risky than conventional tissue biopsies
Question: We’ve all heard of a tissue biopsy, in which a sample of a patient’s cancer is surgically removed for analysis. But what is a “liquid biopsy”?
Answer: A team of international researchers, including those from the Phoenix-based Translational Genomics Research Institute, or TGen, and Mayo Clinic in Arizona, found that analyzing circulating tumor DNA, or ctDNA, from a patient’s blood could track how their cancer evolves and responds to treatment.
In a study published recently in the journal "Nature Communications," Dr. Muhammed Murtaza of TGen and Mayo Clinic, described an extensive comparison between the results from conventional tissue biopsies and the results from ctDNA analysis of blood samples from a patient with breast cancer.
The researchers followed the patient over three years of treatment.
When patients receive therapy for advanced cancers, especially those that spread to other parts of the body, not all tumors respond the same. However, it has been difficult to study this phenomenon because it is not practical to perform multiple, repeated tissue biopsies.
The recent study showed that ctDNA analysis from blood samples allows researchers to detect cancer mutations from multiple tumors and at different sites within a patient, and track how each of them responds.
This type of blood test — known as a liquid biopsy — is less invasive, less costly and less risky than conventional tissue biopsies, which essentially are minor surgeries.
Obtaining liquid biopsies could occur more frequently, too, thus providing physicians with up-to-date information about how a patient’s cancer might be changing. This, in turn, could help in the selection of the best possible treatments to combat the cancer.
The researchers followed a 42-year-old woman diagnosed with invasive ductal carcinoma — the most common type of breast cancer — that had spread to other parts of her body, including her backbone, chest and liver. Eventually, it spread to her brain and left ovary.
Over the course of her illness, the researchers obtained eight tissue biopsies and nine blood samples for study, including samples obtained at a research autopsy. Their analysis revealed that ctDNA in blood samples tracked mutations that occurred in her cancer as it spread to various parts of her body and identified the tumor sites that developed resistance to therapy.
The results showed that ctDNA, collected through liquid biopsies, provides a dynamic sampling of cancer-cell alterations, reflecting the size and activity of distinct parts of the cancer.
Further, the study results suggest that precise and up-to-date genetic monitoring of changes in a patient’s tumors, through ctDNA analysis, could help inform physicians what type of targeted treatment might be best at each stage of the disease.
Contributors and supporters of this study also included: the University of Cambridge, Cancer Research UK, and Science Foundation Arizona’s Bisgrove Scholars Early Tenure Track Award.
Dr. Muhammed Murtaza is co-director of TGen’s Center for Noninvasive Diagnostics and one of the lead authors of the "Nature Communications" study. He can be reached at mmurtaza@tgen.org.