Liquid Biopsy Offers a Useful Diagnostic Companion for Targeted Therapies
By Celia Spell
Conventional biopsies are invasive, costly, and sometimes impossible to conduct, but they yield valuable information other methods were unable to provide—until now.
Newly developed liquid biopsies allow physicians to access the biochemical and genetic information of a tumor through a simple blood test. The FDA has not approved the technique thus far, but Michael B. Lilly, M.D., Associate Director for Translational Research at MUSC’s Hollings Cancer Center, is confident the technique will be approved in the coming months. Liquid biopsies obtain tumor cells or tumor-derived molecules from the blood, rather than from a direct biopsy of tissue. One type of liquid biopsy isolates circulating tumor DNA (ctDNA) from the blood.
Physicians are finding they can use ctDNA levels in the blood to diagnose and determine the prognosis of a patient while also monitoring the progression of the tumor, as supported by a study published in the February 19, 2014 issue of Science Translational Medicine by Bettegowda et al. The study showed that ctDNA was detectable in more than three-fourths of patients with advanced pancreatic, ovarian, colorectal, bladder, gastro-esophageal, breast, melanoma, hepatocellular, and head and neck cancers. The study also found a correlation between ctDNA levels and patient longevity, with higher levels coinciding with decreased survival.
Dr. Lilly is currently studying the usefulness of liquid biopsies in advanced-stage prostate cancer patients to identify the kinds of gene mutations present. He is also designing a clinical trial of targeted therapy in these patients in which liquid biopsies will identify potential participants.
“The liquid biopsy is a fascinating tool, but it’s not going to replace studying the original tissue itself,” says Dr. Lilly. “The big things are that it’s easy, and it can be repeated.”
One limitation of the conventional biopsy is that it delivers static information, a snapshot of the tumor at the time of the biopsy. Tumors are known to change their molecular make-up as they progress. Physicians can use ctDNA to monitor the patient’s tumor over time, learning about its genetic basis for resistance, using that knowledge to choose targeted gene therapies, and watching for any sign of recurrence.
Another limitation is that the data collected through a conventional biopsy is only indicative of that particular tumor. Patients may have another nodule a few inches away that is genetically different and would require its own biopsy. However, by using ctDNA, physicians can gather information from all the tumors in the body, delivering an overall picture of the genes involved in many cancers.
Rapid advances in genetic sequencing technology have made liquid biopsies clinically feasible. Sensitive methods such as Next-Generation sequencing can detect tiny fragments of ctDNA in a string of normal patient DNA—even when they account for only 0.2 percent of the total DNA (allele frequency).
Studies support the use of the liquid biopsy as an informative technique that could improve treatment choices and increase survival, but there are drawbacks. For one, finding ctDNA in the blood tells the physician that the patient may have a tumor, but it does not provide any information about its location. Liquid biopsies show most promise for enabling early diagnosis and for choosing and assessing treatment for those with metastasized cancer.