anchor "Phase II results of circulating tumor DNA as a predictive biomarker in adjuvant chemotherapy in patients with stage II colon cancer: NRG-GI005 (COBRA) phase II/III study." J Clin Oncol. 2024;42(3 suppl):5 (NRG Oncology; presented at ASCO GI 2024). A randomized US cooperative-group trial in resected low-risk stage IIA colon cancer testing whether ctDNA can select patients for adjuvant chemotherapy. The prespecified phase II analysis was NEGATIVE and the trial was halted under its stopping rules: among the initial ctDNA-positive patients, adjuvant chemotherapy did not increase ctDNA clearance at 6 months relative to observation (clearance 1/9, 11% in the chemotherapy arm vs 3/7, 43% in the control arm). This is directly in scope (stage IIA colon, post-resection ctDNA, adjuvant decision) and an important counterweight to de-escalation enthusiasm: where DYNAMIC (nod_ca77eb54) showed ctDNA-guided withholding of chemotherapy was noninferior, COBRA found no evidence that the converse — giving chemotherapy to ctDNA-positive low-risk stage II patients — clears MRD, cautioning against assuming the escalation direction benefits low-risk stage II disease. Caveats: this is an interim/abstract readout with very small ctDNA-positive numbers at the analysis, the surrogate endpoint was ctDNA clearance (not RFS/OS), and it used the trial's original pre-amendment assay; a full publication is the natural supersede target.

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