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Ability of Assay to Predict Response to Immunotherapy in Patients With Advanced Gastric Cancer

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Key Points

  • Based on results of the Guardant360 assay, patients who were categorized as having a high mutational load had an 83% overall response rate (ORR), compared to an ORR of 7.7% (P = .0014) in those who were not categorized as having a high mutational load.
  • A second blood test performed only 6 weeks after starting pembrolizumab was able to predict treatment failure in most patients months before clinical failure.

Researchers from Samsung Medical Center and Guardant Health, Inc have demonstrated the feasibility of determining a measure analogous to tumor mutation burden, a promising biomarker that may predict patient response to certain immunotherapies, utilizing the Guardant360 assay, a comprehensive liquid biopsy introduced in 2014. Additionally, they showed that this measure in Guardant360 can predict the response to the immune checkpoint inhibitor pembrolizumab (Keytruda) in advanced gastric cancer patients who have already had other lines of treatment. These findings were published by Kim et al in Nature Medicine.

Study Methods and Findings

Researchers developed 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 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. Based on the results of the Guardant360 assay, patients who were categorized as having a high mutational load had an 83% overall response rate (ORR), compared to an ORR of 7.7% (P = .0014) in those who 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 6 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.”

The content in this post has not been reviewed by the American Society of Clinical Oncology, Inc. (ASCO®) and does not necessarily reflect the ideas and opinions of ASCO®.


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