Castle Biosciences Inc. today announced study results from its proprietary multi-analyte test DecisionDx-EC, which is designed to determine which patients with esophageal cancer are likely to respond or not respond to standard pre-surgical chemoradiation therapy. The results were reviewed in a poster presentation at the 50th Annual Meeting of the American Society of Clinical Oncology (ASCO). The data demonstrate the biomarker test's ability to accurately identify two types of patients: those who are likely to respond to pre-surgical chemoradiation therapy (CTRT) and should continue to receive the standard therapy; and those unlikely to respond to CTRT and could instead move rapidly to surgery or other more effective therapies.
"One of the challenges in treating esophageal cancer is knowing that while some patients will have an excellent response to standard pre-surgical chemoradiation, up to 30 percent of patients will not respond to this therapy," said Dr. Sunil Badve, M.D., FRCPath, Professor of Pathology and Laboratory Medicine at the Indiana University School of Medicine, and co-author of the study. "The toxicities associated with chemoradiation treatment are significant and can substantially reduce a patient's quality of life while delaying surgery and the use of potentially more effective therapies. We could use the results from the multi-analyte test to better identify patients who are likely to respond, while avoiding highly toxic therapies in patients for whom they are unlikely to be effective."
Esophageal Cancer Study Results
The DecisionDx-EC test analyzes the localization of three protein biomarkers, NF-kB, Gli1 and SHH, to classify tumors as likely to have a complete response to (pathCR) or likely to have extreme resistance to CTRT (exCTRT). Testing was performed on formalin-fixed paraffin embedded (FFPE) esophageal adenocarcinoma tissue.
This independent multi-center study of 65 patients with locoregional esophageal adenocarcinoma was the second validation study for the DecisionDx-EC test. In this group of patients, the multi-analyte test predicted patients who would experience exCTRT with a 95% specificity, demonstrating a positive predictive value (PPV) of 83% and a negative predictive value (NPV) of 77%.
Importantly, the results also found that the test can accurately predict which patients will experience a complete response to the therapy prior to surgery, and which will likely see no benefit. The DecisionDx-EC test predicted pathCR with a specificity of 87%, PPV of 42%, and NPV of 89%. This aspect of the test was optimized to ensure that potential CTRT responders will not be undertreated.
Rectal Adenocarcinoma Results
Castle Biosciences also presented initial data from a study of its newly developed rectal cancer (RC) test in FFPE samples from 10 patients with rectal adenocarcinoma (RC). Using the same biomarkers as the multi-analyte EC test, the RC test was able to predict exCTRT and pathCR with an overall accuracy of 80%, specificity of 100%, PPV of 100%, and NPV of 71%. Expanded validation of the biomarker test in RC is currently underway.