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Using ctDNA to Predict Response to Chemotherapy in Colon Cancer

By: Hillary Ojeda
Posted: Thursday, March 26, 2020

A prospective phase II/III clinical trial known as NRG-GI005 (COBRA) is exploring whether or not circulating tumor DNA (ctDNA) may be used as a predictive biomarker for patients with stage II resected colon cancer after adjuvant chemotherapy. Van K. Morris II, MD, of The University of Texas MD Anderson Cancer Center, Houston, and colleagues, presented their study design at the 2020 Gastrointestinal (GI) Cancers Symposium in San Francisco (Abstract TPS261).

A total of 1,408 patients with resected stage II colon cancer without traditional high-risk features, who are determined suitable for no adjuvant chemotherapy, will be enrolled in the study. They will be randomly assigned 1:1 into two treatment arms: standard of care/observation (arm A) or prospective testing for ctDNA (arm B). Using a GuardantHealth LUNAR panel, investigators will examine patients’ postoperative blood. Patients in arm A will have their ctDNA status analyzed retrospectively during endpoint analysis. Patients in arm B with ctDNA detected will receive 6 months of adjuvant FOLFOX (fluorouracil, leucovorin, oxaliplatin) chemotherapy.

Primary study endpoints include clearance of ctDNA with adjuvant chemotherapy and recurrence-free survival for “ctDNA-detected” patients treated with or without adjuvant chemotherapy. Secondary study endpoints will be time-to-event outcomes by ctDNA marker status and treatment, prevalence of detectable ctDNA in stage II colon cancer, and rates of compliance with assigned intervention.

For more information on the COBRA trial, visit ClinicalTrials.gov.

Disclosure: The study authors’ disclosure information may be found at coi.asco.org.



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