Researchers from Samsung Medical Center and Guardant Health, Inc. have demonstrated the feasibility of determining a measure analogous to tumor mutation burden (TMB), a promising biomarker that may predict patient response to certain immunotherapies, utilizing the Guardant360® assay, a comprehensive liquid biopsy. Additionally, they showed that this measure in Guardant360 can predict response to pembrolizumab in advanced gastric cancer patients who already had other lines of treatment.
In a paper published in Nature Medicine, researchers describe developing a statistical model to classify mutational load from a database of 10,543 clinical Guardant360 assay samples. They then analyzed the blood of 23 patients with metastatic gastric cancer who were about to be treated with the immune checkpoint inhibitor pembrolizumab, applied the above statistical model, and categorized them into one of three groups, based on whether their respective mutational loads, as identified by utilizing the Guardant 360 assay, were low, moderate, or high. Patients who were, based on the results from the Guardant360 assay, categorized as having a high mutational load had an 83% overall response rate (ORR), compared to an ORR of 7.7% (p = 0.0014) in those that were not categorized as having a high mutational load.
“In our data set, we found that plasma mutational load score was a strong predictor of immunotherapy response,” said Justin Odegaard, MD, PhD, Guardant Health’s senior medical and laboratory director. “This study suggests that by using algorithms trained on thousands of clinical blood samples, Guardant360 can identify a subset of patients who are highly likely to respond to immunotherapies. Another important finding was that a second blood test performed only six weeks after starting pembrolizumab was able to predict treatment failure in most patients months before clinical failure. These are very exciting developments and raise several new lines of inquiry worth pursuing.”
Since its introduction in 2014, the Guardant360 assay has been ordered more than 70,000 times to help inform which therapy may be effective for advanced stage cancer patients with solid tumors. It has been reviewed by more than 70 peer-reviewed publications, which address its analytical validity, clinical validity, and clinical utility. Guardant360 is covered by several private payers, including Cigna and several Blue Cross Blue Shield plans, and will be covered by Medicare starting August 27, 2018.