Reproducibility and clinical concordance of a tumor-informed MRD assay in patients with resected colorectal cancer from the DYNAMIC trials.

26 Background: Haystack MRD is a highly accurate, tumor-informed ctDNA assay designed for minimal residual disease (MRD) detection. To evaluate clinical performance and inter-laboratory reproducibility, retrospective testing of samples from early-stage colorectal cancer (CRC) patients enrolled in the randomized DYNAMIC and DYNAMIC-III trials was performed. Methods: Residual specimens from 59 patients (51 stage II, 8 stage III CRC) with annotated clinical outcomes were analyzed using the CLIA-validated Haystack MRD assay, which targets up to 50 tumor-informed, patient-specific variants derived from whole-exome sequencing of tumor and matched normal DNA. Testing was performed on 60 cell-free DNA (cfDNA) samples from 59 unique patients, containing a median of 3,800 genomic equivalents from plasma collected post-operatively (n=40) and post-adjuvant chemotherapy (n=20). Concordance of MRD results with clinical recurrence was assessed. Orthogonal validation was also conducted to evaluate reproducibility across two independent CLIA-certified laboratories: Quest Diagnostics Oncology Center of Excellence (Lewisville, TX) and Haystack Oncology (Baltimore, MD). Results: All 60 samples tested with Haystack MRD in parallel at the two sites yielded concordant MRD results (100% agreement). MRD positivity was observed in 10 of 12 samples from patients who experienced clinical recurrence, while 48 samples from patients who remained recurrence-free tested MRD-negative (sensitivity: 83%; specificity: 100%; positive predictive value PPV: 100%; negative predictive value NPV: 96%). Quantitative ctDNA measurements were between 0.32 (min) and 316.21 (max) mean ctDNA molecules/ml and were highly correlated across sites (Pearson correlation coefficient = 1.000; p<0.0001), supporting strong inter-laboratory reproducibility. Additional testing is ongoing. Conclusions: This study provides both clinical and orthogonal validation of the Haystack MRD assay using well-characterized specimens from the DYNAMIC trials. Results demonstrate high concordance with clinical recurrence outcomes and reproducibility across independent laboratories. These findings support the use of Haystack MRD as a robust approach for MRD detection following curative-intent treatment in stage II/III CRC, with potential to guide adjuvant therapy decisions and enable proactive, ctDNA-informed monitoring.